KR100682486B1 - Method and apparatus for distinguishing fingerprint replica - Google Patents

Abstract

A method and a device for distinguishing a fingerprint replica are provided to distinguish diverse types of the fingerprint replica by applying both an absorption/scattering type distinguishing methods/devices and an external light type distinguishing method/device to one device and by checking over gray-level distribution for surface image of a contacted object. The first light source(210) performs scattering type fingerprint obtainment. The second light source(212) performs absorption type fingerprint obtainment. The third light source(214) irradiates external light. A light source controller(220) operates the light sources. An image detector(230) detects the first image output from a fingerprint output surface of a prism(200) when the first light source is turned on, detects the second image output from the fingerprint output surface when the second light source is turned on, and detects a surface image of a finger contacted to a fingerprint input window when the third light source is turned on. The first and second fingerprint replica determiner(240,250) determines the fingerprint replica if brightness of the first and second image is not inverted, or gray-level distribution of the third image corresponds to the fingerprint replica.

Description

Imitation fingerprint identification method and apparatus {Method and apparatus for distinguishing fingerprint replica}

1 is a block diagram of an imitation fingerprint identification device according to the prior art.

FIG. 2 is a biofingerprint image acquired with the apparatus of FIG.

3 is an imitation fingerprint image acquired by the apparatus of FIG.

4 is a block diagram of an imitation fingerprint identification device according to another prior art

FIG. 5 is a bio fingerprint image and gray level distribution acquired by the apparatus of FIG.

FIG. 6 is a fake fingerprint image and gray level distribution acquired with the apparatus of FIG.

7 is a flowchart illustrating a method of identifying a fingerprint according to the present invention.

8 to 10 is a conceptual diagram illustrating a further embodiment in the method for identifying a fingerprint according to the present invention.

11 to 13 are grey-level distribution diagrams of an acquired image for explaining a part of the imitation fingerprint identification method according to the present invention.

14 is a block diagram of an imitation fingerprint identification apparatus according to the present invention.

15 and 16 are conceptual views illustrating another embodiment of the apparatus for identifying a fingerprint according to the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a system for identifying a biometric fingerprint and a fake fingerprint in a fingerprint recognition device, and to a technology configured to identify a fake fingerprint of any type.

As fingerprint recognition devices are widely used in personal authentication fields such as access authentication and payment, security enhancement is required. In the field requiring security, in particular, many fingerprint recognition algorithms and algorithms for coping with fingerprints have been applied to enhance the accuracy of fingerprint recognition. Accordingly, fingerprint replication technology is becoming more sophisticated.

Applicant has developed a variety of technologies for the device and method for distinguishing the biological fingerprint and the imitation fingerprint has been registered and applied for a patent. The representative ones are as follows.

Patent Application No. 2004-89877 (filed Nov. 5, 2004)

This prior art is to accurately identify the fingerprint printed on the film, etc., which is difficult to solve the existing imitation fingerprint identification method, and in the case of the bio fingerprint, the contrast of the resulting image of the scattering and absorption type is inverted from each other, but the film In the case of the imitation fingerprint printed on the paper, it was designed based on the fact that the fingerprint acquisition device obtains the same result image (no contrast is reversed) regardless of scattering or absorption type. The present invention uses both of these characteristics to apply both scattering and absorption mechanisms to a fingerprint acquisition device to compare two images acquired by each method to determine whether it is a biometric fingerprint or a fake fingerprint.

This will be described in detail with reference to FIG. 1. Fingerprint acquisition device according to the prior art, the prism 10 including a fingerprint input window 12 to which the fingerprint to be acquired is in contact and a fingerprint exit surface 14 to which the fingerprint image is emitted; A first light source 20 installed at a position irradiating light 22 at an angle totally reflected from the fingerprint input window 12 of the prism 10; A second light source 30 installed at a position irradiating the light 32 at an angle that is not totally reflected from the fingerprint input window 12 of the prism 10; A light source switching unit 40 for sequentially operating the first light source 20 and the second light source 30; A focusing lens 50 for focusing the first image and the second image emitted from the fingerprint output surface 14 of the prism 10 when the first light source 20 is turned on and the second light source 30 is turned on; Image sensor 60 for detecting an image: When the first image signal and the second image signal detected by the image sensor 60 has a value of the inverted valleys and ridges of both images (see Fig. 2) ) Is determined as a biofingerprint, and when the bone and the ridge of both images have a value in which the ridge is not inverted (see FIG. 3), the image comparator 70 determines to be a fake fingerprint.

In the above structure, the first light source 20 is a light source for implementing the absorption equation, and the second light source 30 is a light source for implementing the scattering equation. The configuration is characterized in that both absorption and scattering operation in one optical system is made.

Patent No. 442583 (registered July 22, 2004)

Referring to Fig. 4, the imitation fingerprint identification device includes a light source 54 for irradiating external light so that light passes through an inner surface adjacent to the surface of the contact body 52 in contact with the fingerprint input window 50; A light emission controller 53 for controlling this on and off; The external light incident from the light source 54 passes through the inside of the contact body 52 and then exits the outside of the contact body 52 to detect an image formed by the image sensor 55 to detect the surface of the contact body 52. A contact surface image obtaining unit 56 which acquires an image; An image analyzer 57 analyzing the image acquired by the contact surface image acquisition unit 56; It is composed of a fake fingerprint identification unit 58 for determining whether the fingerprint obtained from the contact body 52 is a biometric fingerprint or a fake fingerprint according to the image analysis result of the image analyzer.

The principle of the prior art is that when the contact body 52 is a biofingerprint, since the degree of light attenuation inside is large, the light is rapidly attenuated and extinguished as the light progresses therein. Since it transmits the light, the phenomenon that the difference between the incident light amount and the transmitted light amount is small is used. That is, in the case of the biofingerprint, the light incident on the inside of the contact is rapidly attenuated and transmitted, so that the gray level of the contact surface image acquired from the outside gradually decreases toward the position away from the light source (the image (a) of FIG. 5). And gray level distribution (b)). On the other hand, in the case where the contact is a dummy fingerprint, the light incident on the inside of the contact can be transmitted at a constant intensity within the dummy fingerprint, so that the gray level of the contact surface image acquired from the outside becomes almost constant anywhere (Fig. 6). See also image (A) and gray level distribution (B). In the prior art, it is determined whether a contact is a bio fingerprint or a fake fingerprint by analyzing the difference in the gray level distribution of the contact surface image.

In the above, the former prior art is a technique applicable to the case of the imitation fingerprint of the form printed on a film or the like, the latter prior art is a technique applicable to the case of the imitation fingerprint manufactured in the form of a finger directly from a material such as silicone rubber. In other words, when the imitation fingerprint printed on a film or the like is input, the latter technique cannot determine whether the imitation fingerprint is input, and when the imitation fingerprint produced in the form of a finger is input, the imitation fingerprint is used by the former technique. It is not possible to determine whether it is a fingerprint.

In order to identify any form of imitation fingerprint, the present invention compares the two methods introduced above (by determining the gray level distribution of the surface image of the contact, and comparing the two images acquired by the absorption and scattering equations). By devising a method and a system for identifying a fingerprint that employs all of them, it is possible to respond more effectively to the sophisticated fingerprint reproduction.

Accordingly, an object of the present invention is to apply the imitation fingerprint identification method / device by the absorption type, scattering expression and the imitation fingerprint identification method / device by external light irradiation in one system, the imitation fingerprint which can identify various types of imitation fingerprints It is to provide an identification method and apparatus.

According to an aspect of the present invention, there is provided a method for determining whether a contact is a biometric fingerprint or a fake fingerprint by acquiring an image of an object (hereinafter referred to as "contact body") in contact with a fingerprint input window of a fingerprint acquisition device.

(1) acquiring a first image by an optical scattering method for a contact placed on a fingerprint input window, and acquiring a second image by an optical absorption method for a contact, and comparing the images, (2) the first image And comparing the second image to determine that the contrast of the two images is not inverted. (3) comparing the first and second images to invert the contrast of the two images. The external light is irradiated to transmit light along the inner side adjacent to the contact surface of the contact, and detects that the external light irradiated to the contact passes through the inside of the contact and then exits to the outside of the contact. Acquiring a surface image (third image), (4) analyzing a gray level distribution of the acquired third image, and determining that the contact is a biofingerprint if the gray level distribution corresponds to a biofingerprint; Visual The ray-level distribution Having a gray level distribution in the artificial fingerprint consists of a step of determining that the artificial fingerprint contact the body.

In the step (2), when the sum of the differences between the gray levels of the first and second images is larger than the reference value, it is determined that there is a contrast in contrast between the two images, and the gray level in the predetermined region of the first and second images is determined. When the sum of the differences is less than the reference value, it is characterized by the imitation fingerprint without contrast contrast of both images.

In the step (4), a plurality of sections may be set in a direction away from the point where the external light is incident on the contact body (hereinafter, the incident position) in the gray level distribution chart for each distance of the third image. Detecting the maximum value of the gray level, and determining the biological fingerprint when the maximum value of the gray level of each section decreases as the maximum value of the detected gray level is far from the point where the external light is incident. It is composed.

As another feature of the present invention, the step (4) may include: setting a plurality of sections in a direction away from an incident position at which external light is incident on the contact point in the gray level distribution diagram for each distance of the third image; Setting a reference range of the maximum gray level for each section, calculating a maximum value of the gray level for each set section, and comparing the calculated maximum value of the gray level for each section with a set reference range If it is within the reference range, it is determined that the bio fingerprint.

As another feature of the present invention, the step (4) may include: setting a plurality of sections in a direction away from an incident position at which external light is incident on the contact point in the gray level distribution diagram for each distance of the third image; Setting an average value reference range of gray levels for each section, calculating an average value of gray levels in each of the set sections, and comparing the average value of the calculated gray levels for each section with a set reference range If included within, determining to be a biofingerprint.

On the other hand, as another configuration of the method according to the present invention described above, in addition to the method of acquiring the third image separately when the contact is determined to be a fake fingerprint after comparing the first image and the second image as described above, In the invention can be implemented in a variety of ways. For example, in a state where the first, second, and third images are first obtained, the contrast between the two images is inverted or the gray of the third image is compared by comparing the first and second images among the three images. When the level distribution is analyzed and the gray level distribution corresponding to the bio fingerprint is determined, it is determined that the contact is a bio fingerprint, and the contrast between the first and second images is not inverted or the third image is compared. If the gray level distribution has a gray level distribution corresponding to the dummy fingerprint, it may be determined that the contact body is a dummy fingerprint. The specific method of each determination in this case can be made in the same manner as described above for each feature.

On the other hand, the imitation fingerprint identification device according to the present invention, a prism including a fingerprint input window and a fingerprint exit surface from which the image of the input fingerprint is emitted, and emits light at an angle that is not totally reflected from the inner surface of the fingerprint input window of the prism A first light source installed at a position for performing scattered fingerprint acquisition, a second light source installed at a position for emitting light at an angle totally reflected from an inner surface of the fingerprint input window of the prism, and performing an absorption fingerprint acquisition; A third light source for irradiating external light to transmit light along an inside adjacent to the surface of the contact in contact with the fingerprint input window, and a light source controller for selectively operating the first light source, the second light source, and the third light source; When the first light source is turned on by the light source control unit, the first image emitted from the fingerprint output surface of the prism is detected. When the second light source is turned on, the fingerprint output of the prism is detected. An image detector for detecting a second image emitted from the second image source and detecting a surface image (third image) of the contact body in contact with the fingerprint input window of the prism when the third light source is turned on; A first imitation fingerprint judgment unit that processes the first image and the second image and outputs a result of imitation fingerprint determination when the contrast between the two images is not inverted from each other; and the first and second images in the first imitation fingerprint determination unit In the case where the contrast of the image is analyzed as being inverted, the determination result is analyzed by analyzing whether the third image has a gray level distribution corresponding to a bio fingerprint or a gray level distribution corresponding to a fake fingerprint from the gray level distribution of the third image. It consists of a second imitation fingerprint judgment unit for outputting.

The first imitation fingerprint determining unit comprises means for calculating a sum of differences of gray levels in a predetermined region of each image of the first image and the second image, and when the sum of the differences of gray levels of both images is larger than a reference value, It is judged that there is a contrast inversion, and when the sum of the differences of the gray levels in the predetermined area is smaller than the reference value, it is constituted by means of the imitation fingerprint without the contrast inversion of both images.

The second imitation fingerprint determiner detects a maximum value of the gray level in each section set in a direction away from the incident position where external light is incident on the contact in the gray level distribution chart for each distance of the third image, and detects the detected gray level. Means for discriminating with the biofingerprint when the maximum value of the gray level for each section decreases as the maximum value of the further away from the point at which external light starts to be incident.

According to another feature of the invention, the second imitation fingerprint determiner, the maximum value of the gray level in each section set in the direction away from the incident position where the external light is incident on the contact point in the gray level distribution chart for each distance of the third image Means for calculating the maximum value of the gray level for each of the set sections, and comparing the calculated maximum value of the gray level with the set gray level maximum value reference range to determine that it is a bio fingerprint. It includes.

According to another feature of the invention, the second imitation fingerprint determiner, the maximum gray level in each section set in the direction away from the incident position where the external light is incident on the contact in the gray level distribution of each distance of the third image. Means for detecting a value, calculating an average value of gray levels in each of the set intervals, and comparing the calculated gray level average value with a set gray level average value reference range to determine that the fingerprint is a biofingerprint It includes.

In addition, the path of the light of the second light source to the inside of the prism, it is preferable that the light from the inside of the prism is not reflected, and further includes a semi-reflective projection film to allow the light of the second light source to enter the prism, Further, it is more preferable that the semi-reflective film is subjected to a diffusion plate treatment so that light from the second light source diffuses into the prism and is incident.

On the other hand, the apparatus according to the present invention, instead of sequentially acquiring the first, second image and the third image, as described above, the first and second imitation fingerprint judging unit, to determine whether the imitation fingerprint, first, second After all of the second and third images have been acquired, the images may be processed to determine whether the single fingerprint is determined by the single fake fingerprint judgment unit. The configuration of the present invention device in this case is as follows.

A prism including a fingerprint input window and a fingerprint exit surface on which an image of the input fingerprint is emitted; A first light source installed at a position that emits light at an angle that is not totally reflected from an inner surface of the fingerprint input window of the prism to perform scattered fingerprint acquisition; A second light source installed at a position to emit light at an angle totally reflected from the inner surface of the fingerprint input window of the prism to perform absorption type fingerprint acquisition; A third light source irradiating external light to transmit light along an interior adjacent to a surface of the contact body contacting the fingerprint input window; A light source controller for selectively operating the first light source, the second light source, and the third light source; When the first light source is turned on by the light source control unit, a first image emitted from the fingerprint exit surface of the prism is detected, and when the second light source is turned on, a second image exited from the fingerprint exit surface of the prism is detected. An image detector detecting a surface image (third image) of the contact body in contact with the fingerprint input window of the prism when the third light source is turned on; Among the images, when the contrast of both images is inverted by comparing the first and second images or the gray level distribution of the third image is analyzed to have a gray level distribution corresponding to the bio fingerprint, the contact is a bio fingerprint. A counterfeit which determines that the contact is a dummy fingerprint when the contrast between the first and second images is not reversed or when the gray level distribution of the third image has a gray level distribution corresponding to the dummy fingerprint. Fingerprint Verdict.

In this configuration, the specific action of the determination of whether the biometric fingerprint or the imitation fingerprint in the imitation fingerprint determination unit is the same as that of the first and second imitation fingerprint determinations described above.

Hereinafter, with reference to the drawings will be described a preferred embodiment of the imitation fingerprint identification method and apparatus according to the present invention. First, a method for identifying a fingerprint according to the present invention will be described. According to an embodiment of the present invention described below, a part of the configuration of the present invention, that is, the first image and the second image are first acquired and analyzed, and when the contact body is determined to be a fake fingerprint, the third image is acquired again. A preferred embodiment of the method and apparatus for determining whether a fake fingerprint is present is introduced. The configuration for acquiring all of the first, second, and third images disclosed above and determining whether the contact is a fake fingerprint or a bioprint from them can be easily understood from the individual description of the following embodiments. There will be.

7 is a method for identifying a fake fingerprint according to the present invention, that is, a method for determining whether a contact is a biometric fingerprint or a fake fingerprint by acquiring an image of an object (hereinafter referred to as "contact body") in contact with a fingerprint input window of a fingerprint acquisition device. Is the flow of processing.

(1) acquiring a first image by optical scattering for a contact placed on a fingerprint input window [102], and acquiring a second image by optical absorption with a contact [104] and comparing these images [106]. ].

The first image is acquired by the scattering equation and the second image is acquired by the absorption equation. In terms of the device, it is preferable that the scattering equation and the absorption equation are commonly implemented in one optical system, but the present invention is not limited thereto. In addition, there is no limitation on the acquisition order of the scattered image and the absorbed image. However, the imitation fingerprint identification method and apparatus according to the present invention discloses the imitation fingerprint identification function, but in reality, it is also necessary to perform the basic function that should perform authentication on the fingerprint image from the bio fingerprint. Therefore, in the case of a system for acquiring a fingerprint image to be used for fingerprint authentication in a scattering manner, the quality of the scattering fingerprint image should be prioritized.

(2) comparing the first and second images and determining that the contact is a fake fingerprint when the contrast between the two images is not inverted [107].

As described above, in the absorption type fingerprint acquisition apparatus, light absorption occurs in the ridge portion, so that the ridge of the fingerprint is dark and the valley is bright in the acquired image. On the other hand, in the scattering fingerprint acquisition device, light scattering occurs in the ridge, so that the ridge is bright and the bone is dark, and the absorption image and the contrast image are acquired. In FIG. 2, the contrast state of the fingerprint image may be confirmed. FIG. 2A illustrates a biofingerprint image acquired by a scattering equation, and FIG. 2B illustrates a biofingerprint image acquired by an absorption fingerprint acquisition device.

On the other hand, in the case of the imitation fingerprint printed on a film or the like, whether the acquired image is an absorption type or a scattering type, the contrast is obtained without being inverted from each other. In the case of imitation fingerprints printed on the film, light is absorbed in the dark areas (mainly black as ink parts) covered with the absorbing material, regardless of absorption or scattering, and appears dark in the light areas (the base material of the film). Appears bright. Therefore, in the case of the imitation fingerprint of the type printed on the film, an image of the same type is acquired whether it is an absorption type or a scattering type. Fig. 3 illustrates an image obtained from a fake fingerprint in a form printed on a film. 3A is an image acquired by the absorption type fingerprint acquisition device, and (b) illustrates an image obtained by the scattering type fingerprint acquisition device. It can be seen that there is no inversion of contrast compared to FIG. Since the images of the biological fingerprint and the imitation fingerprint obtained by the absorption type and the scattering type fingerprint acquisition device are different from each other, using such a property makes it possible to completely identify the imitation fingerprints printed on the film like the method of the present invention.

By using this principle, when the dummy fingerprint is identified by comparing the first image and the second image, the sum of the differences of the gray levels of the two images is calculated by calculating the sum of the differences of the gray levels in the predetermined region of each acquired image. If it is larger than this reference value, it is determined as a bio fingerprint, and if the sum of the differences of gray levels in a predetermined area is smaller than the reference value, a method of determining as a fake fingerprint can be used. For example, the sum of the differences of gray levels can be obtained by the following equation. That is, the difference between gray levels for pixels corresponding to the same position in a predetermined area is calculated, and the sum of differences in gray levels for all pixels in the predetermined area is obtained.

G _a (a, b): Gray level at coordinates (a, b) in an image acquired by absorption

G _s (a, b): Gray level at coordinates (a, b) in the image acquired by the scattering equation

j, k: starting coordinates of the predetermined area

(m + 1) x (n + 1): the size of the predetermined area

Summarizing the above description, as described in the above-mentioned prior art item, the image acquired by the scattering equation and the image acquired by the absorption equation are obtained because the contrast of the ridges and the bones is obtained by inverting each other in the case of the biofingerprint. The image and the second image may be compared to determine whether the fingerprint is a biometric fingerprint or a fake fingerprint. More specifically, the sum of the differences between the gray levels in the predetermined areas of the first and second images is calculated, and when the sum of the differences between the gray levels is larger than the reference value, it is determined that there is a contrast inversion. When the sum of the differences in the gray levels in the predetermined region of the two images is smaller than the reference value, it will be possible to determine that the dummy fingerprint has no contrast inversion.

(3) When the contrast between the first and second images is inverted from each other [109], external light is irradiated to transmit light along the inner side adjacent to the contact surface of the contact, And detecting a surface image (third image) of the contact by detecting that the irradiated external light passes through the inside of the contact and then exits to the outside of the contact [110].

In this step, when the contrast between the first and second images, the contrast is reversed, in order to check again whether it is another type of imitation fingerprint, to determine the imitation fingerprint by external light irradiation, one of the prior art described above Steps to further apply the method. As described above, the technology for obtaining a transmission image by irradiating the surface of the finger fingerprint with external light is a technology that has been previously filed and patented by the present applicant. Here, the external light is preferably invisible light such as infrared rays, but is not necessarily limited thereto. In addition, the light source is preferably installed hidden in the apparatus so that the user is not visible. This is to minimize the possibility of fraudulent users taking other means to overcome the countermeasures when they are found to be a device for determining a counterfeit fingerprint.

(4) analyzing the gray level distribution of the acquired third image (i.e., the surface image acquired by external light irradiation) [112], and if the gray level distribution corresponds to the bio fingerprint, it is determined that the contact is a bio fingerprint [ 114] If the gray level distribution of the third image has a gray level distribution corresponding to the dummy fingerprint, finally determining that the contact is a fake fingerprint [108].

The gray level distribution of the third image is analyzed to determine whether the contact is a biometric fingerprint or a fake fingerprint, as shown in FIGS. 5 and 6, as the distance from the point where external light is incident on the surface of the contact is increased for each section. The reduction in the maximum gray level can be achieved by identifying other characteristics between the biometric fingerprint and the imitation fingerprint.

That is, referring to FIGS. 4 and 5, it can be seen that a predetermined section is set in the + X axis direction from the point O at which light is incident on the contact body 52. In addition, it can be seen that there are maximum values P1, P2, P3, ..., Pn of gray levels in each section. If the maximum values of gray levels P1, P2, ..., Pn in each interval 1, 2, ..., n are detected and the relationship of P1> P2> ...> Pn is established between these maximum values, Can be determined as a bioprint, otherwise it can be determined as a fake fingerprint (see Fig. 6). Here, since only the gray level in the direction away from the light incidence point of the contact can be detected, the object of the present invention can be attained. Therefore, the analysis direction for each section is sufficient as about one line in the direction of the arrows in FIGS. 5 and 6.

On the other hand, even when using the imitation fingerprint identification method by the external light irradiation as shown in Figures 4 to 6, in the case of the imitation fingerprint of a specific material, as shown in Figure 8, the fingerprint image of the flat window of the fingerprint input window 50 Even when the contact body 51 is contacted away from the light source 54 by a distance d from the contact limit line 62, the gray level distribution of the third image for the imitation fingerprint is similar to the gray level distribution of the bio fingerprint as shown in FIG. (Comparing the gray level distribution of FIG. 5 and the distribution of FIG. 9 is likely to be similar in general). That is, the gray level distribution of the acquired image "when a dummy fingerprint having a specific light transmitting property is contacted a certain distance away from the fingerprint input window" is obtained by contacting the "bioprint which is shown in FIG. 5 in accordance with the contact limit line of the fingerprint input window." In this case, there is a possibility of being misidentified as the gray level distribution of the acquired image.

In order to solve this problem, that is, in order to solve the identification error that occurs when the contact is touched away from the contact limit line of the fingerprint input window, the gray level distribution of the fake fingerprint and the gray level distribution of the biofingerprint are compared, but offset from the contact limit line. By performing the comparison from the position, the counterfeit fingerprint was determined even in the case where the fingerprint was contacted away from the fingerprint input window. Specifically, as described with reference to FIG. 8, the biofingerprint when the biofingerprint finger 51 is contacted away from the light source 54 by a distance d from the fingerprint image contact limit line 62 of the fingerprint input window 50. The gray level distribution of the image is as shown in FIG. Here, during the distance d from the contact limit line 62, the incident light passes as it is, and there is a section 72 where there is no change in the gray level, and thereafter, a normal level distribution 74 as in FIG. 2 occurs. On the other hand, in the case of the imitation fingerprint, as soon as the section 64 through which the light passes as it is, as shown in FIG. 9, the light does not transmit and the gray level falls down (66 sections). Therefore, the gray level distribution when the biological fingerprint is touched away from the contact limit line of the fingerprint input window and the gray level distribution when the fake fingerprint is touched away from the contact limit line of the fingerprint input window are clearly different. In order to use such a difference, in the present invention, the start position of the process of comparing the maximum value of the gray level for each section described above to identify the counterfeit fingerprint is a contact limit line as shown in FIG. It is determined as a position away from the x axis by a predetermined distance. Hereinafter, this position is referred to as "offset distance Lo" (see Figs. 11 to 13).

As described above, in the process of comparing the distribution of gray levels for each section on the x-axis with respect to the gray level distribution of the object in contact with the fingerprint input window, if the comparison process starts from a position separated by Lo from the contact limit line, FIG. Since the imitation fingerprint gray level distribution as shown in FIG. 9 is compared with the bio fingerprint gray level distribution as shown in FIG. 10, the problem of identification error that occurs when a specific imitation fingerprint is contacted away from the contact limit line as described above is solved. To this end, in the third image analyzing step [112], the light source 54 is applied to the remaining contact surface except for a predetermined distance (offset distance Lo) from the start position (see No. 62 of FIG. 8) of the fingerprint input window 50 to which the light source 54 is irradiated. Only for the distribution of gray levels present.

Various methods of determining whether the fingerprint is a biometric fingerprint or a fake fingerprint by analyzing the third image acquired from the contact using this method will be described.

First, a plurality of sections are set in a direction away from the point where the external light is incident on the contact body (hereinafter, the incident position) in the gray level distribution chart for each distance of the third image, and the maximum value of the gray levels in each of the set sections. And detecting the biometric fingerprint when the maximum value of the detected gray level decreases as the maximum value of each gray level decreases as the maximum value of the detected gray level becomes farther from the point where external light starts to enter. Can be. Specifically, in this method, as shown in FIG. 11, the distance away from the incident position ("62" in FIG. 5) where external light is incident on the contact in the gray level distribution of the contact surface image by distance (x-axis direction). Set a plurality of sections (L1, L2, L3, ..., Ln), except for a predetermined distance (Lo, offset distance) from the incident position 62, and for each of the set section of the third image Calculating the maximum values P1, P2, P3, ..., Pn of the gray levels, and if the relationship of P1> P2> P3> ...> Pn is established between the calculated maximum gray levels, The contact consists of determining that it is a biofingerprint, otherwise it is a fake fingerprint. The distribution of gray levels as shown in FIG. 11 is for the biofingerprint, and in the case of the imitation fingerprint, the gray levels as shown in FIG. 9 can be distinguished. That is, in the case of the imitation fingerprint, since the third image has a gray level distribution as shown in FIG. 9, the maximum value of the gray level is almost constant from the interval after the offset distance Lo (d in FIG. 9) over the entire interval. Therefore, since the relationship of P1> P2> P3> ...> Pn does not hold between the maximum gray level of each section, a counterfeit fingerprint can be determined.

In the second method, as in the first method, after setting the plurality of sections in a direction away from the incident position where external light is incident on the contact point in the gray level distribution diagram for each distance of the third image, the set angle Setting a reference range of the maximum value of the gray level for each section, calculating a maximum value of the gray level for each set section, and comparing the calculated maximum value of the gray level for each section with the set reference range If within the range may include determining that the fingerprint. It demonstrates concretely. Referring to FIG. 12, the contact surface image, i.e., a plurality of distances (x-axis directions) away from the incident position ("62" in FIG. 4) where light is incident on the contact point in the gray level distribution diagram according to the distance of the third image. Setting the sections L1, L2, L3, ..., Ln, excluding a predetermined distance Lo from the incident position 62, and setting the reference value Rp1, Setting Rp2, Rp3, ..., Rpn), calculating maximum values P1, P2, P3, ..., Pn of gray levels for each of the set sections, and calculating the respective sections. And comparing the maximum value of the gray level to a predetermined reference range Rp1, Rp2, Rp3, ..., Rpn, and determining that the fingerprint is a biofingerprint if it falls within the reference range.

In a third method, after setting a plurality of sections in a direction away from an incident position where external light is incident on a contact in a gray level distribution chart of distances of a third image, the average value reference range of gray levels for each set section is determined. The step of setting the; and calculating the average value of the gray level in each of the set section, and comparing the average value of the calculated gray level for each section with the set reference range to be a bio fingerprint And determining. In this method, as shown in Fig. 13, the average value of gray levels is used instead of the maximum value of gray levels for each section. That is, a plurality of sections L1, L2, L3, in a direction away from the incident position (“62” in FIG. 4) where light is incident on the contact point (“62” in FIG. 4) in the gray level distribution chart according to the distance of the contact third image. Ln), but excluding a predetermined distance Lo from the incident position 62, and reference ranges Rm1, Rm2, Rm3, ..., of the average value of the gray level for each set interval. Rmn), calculating average gray level values M1, M2, M3, ..., Mn for each of the set sections, and calculating the average gray level M1, calculated for each section. Comprising: M2, M3, ..., Mn is compared with a preset reference range (Rm1, Rm2, Rm3, ..., Rmn) and is determined to be a bio fingerprint when it falls within the reference range.

Next, an example of an apparatus configuration to which the above method can be applied will be described.

Fig. 14 shows a configuration of an imitation fingerprint identification device according to the present invention, and is configured to implement the above-described method of the present invention as one optical system. In the optical fingerprint acquisition device, the difference between the absorption type and the scattering type device is distinguished by whether or not the light is incident on the fingerprint input window at an angle causing total internal reflection. Therefore, in order to implement this as one optical system, as shown in FIG. 14, two first and second light sources 210 and 212 are installed in one prism 200 so that a scattering equation and an absorption equation can be simultaneously implemented. In addition, the third light source 214 is installed to irradiate light to the surface of the finger in contact with the fingerprint input window of the prism 200 in order to irradiate the external light.

Referring to Figure 14 in more detail, the fingerprint acquisition device according to the present invention is

A prism 200 including a fingerprint input window 202 for contacting a fingerprint to be acquired and a fingerprint exit surface 204 for outputting a fingerprint image; A first light source 210 installed at a position that emits light at an angle that is not totally reflected from the fingerprint input window 202 of the prism 200 to perform scattered fingerprint acquisition; A second light source 212 installed at a position that emits light at an angle totally internally reflected from the fingerprint input window 202 of the prism 200 to perform absorption type fingerprint acquisition; A third light source 214 for irradiating external light to transmit light along an interior adjacent to the surface of the contact in contact with the fingerprint input window 202; A light source controller 220 for selectively operating the first light source 210, the second light source 212, and the third light source 214; When the first light source 210 is turned on by the light source controller 220, the first image emitted from the fingerprint output surface 204 of the prism is detected. When the second light source 212 is turned on, the prism is detected. The second image emitted from the fingerprint output surface 204 of the sensor is detected, and when the third light source 214 is turned on, the contact is made to contact the fingerprint input window 202 visible through the fingerprint output surface 204 of the prism. An image detector 230 for detecting a surface image (third image) of the sieve; A first imitation fingerprint determiner 240 that processes the first image and the second image detected by the image detection unit 230 and outputs a result of imitation fingerprint determination when the contrast between the two images is not inverted; As a result of the analysis of the first imitation fingerprint determiner 240, when the contrasts of the two images are inverted from each other, the gray level distribution corresponding to the biological fingerprint is obtained from the gray level distribution of the third image. A second imitation fingerprint determiner 250 for analyzing whether the image has a gray level distribution corresponding to the imitation fingerprint and outputting a determination result; The main control unit transmits a control command signal to the light source control unit 220, the image detection unit 230, the first imitation fingerprint determination unit 240, and the second imitation fingerprint determination unit 250 and receives a processing result signal therefrom ( 260).

A triangular prism may be used as the prism 200, but it is not necessarily a triangular prism. Conventionally, parallelograms or trapezoidal prisms are also used. Although FIG. 14 does not show the physical structure for supporting the prism 200, the light sources 210, 212, and 214, and the image detector 230, the mechanism for supporting these components is readily apparent to those skilled in the art in various ways. Since it may carry out, it does not describe concretely.

14 again, the first light source 210 is for implementing a scattering fingerprint acquisition device, in which light emitted from the light source can be totally reflected on the inner side of the fingerprint input window 202 of the prism 200. It is installed on condition. Accordingly, the position of the first light source 210 may vary depending on the shape of the prism 200, the refractive index of the prism material, the size or shape of the entire optical system, and the like. The scattered fingerprint acquisition device itself is well known and will be apparent to those skilled in the art.

The second light source 212 is for implementing an absorption type fingerprint acquisition device, and is installed at a position that can be scattered as much as possible on the contact surface of the contact without being totally reflected on the inner surface of the fingerprint input window 202. The position of the second light source 212 may also be changed depending on the form or configuration of the system. Absorptive fingerprint acquisition devices are also well known to those skilled in the art.

Unlike the first and second light sources, the third light source 214 is a light source for irradiating external light to the contact surface of the direct contact without passing through the inside of the prism 200. The position of the third light source 214 is provided at a position to irradiate external light so that light is transmitted in the transverse direction along the inner side of the contact surface of the contact body which is in contact with the fingerprint input window 202.

The light source controller 220 is for selectively operating the first light source 210, the second light source 212, and the third light source 214. According to the present invention, in order to identify the imitation fingerprint, a fingerprint image (first image) by a scattering equation, a fingerprint image (second image) by an absorption formula, and a surface image (third image) of a contact body should be acquired. Since one optical system is used, all of the first to third images cannot be acquired at the same time. Therefore, the first to third light sources should be sequentially turned on for the sequential image acquisition. The lighting sequence of the light source that the light source controller 220 selectively operates is arbitrary. However, since the imitation fingerprint identification apparatus according to the present invention basically has to perform a fingerprint authentication function prior to the function of imitation fingerprint identification, it will be designed by those skilled in the art in a manner to obtain a good image quality for fingerprint authentication.

In FIG. 14, the image detector 240 includes a focusing lens 232 and an image sensor 234. In addition, other components may be included. However, since the image detector 240 is an essential component in the optical fingerprint image capturing apparatus, a detailed description thereof will be omitted.

In the first imitation fingerprint determiner 240, the first image acquired when the first light source 210 is turned on (that is, the image acquired by the scattering equation) and the second image acquired when the second light source 212 is turned on. Images (ie, images acquired by absorption) are compared to analyze whether the contrast of both images is inverted or not. When a signal indicating that there is no inversion of contrast between the first image and the second image is output from the first imitation fingerprint determiner 240, the main control unit 260 determines that the contact body is a imitation fingerprint printed on a film or the like, and is pre-programmed. (Eg, system shutdown, re-entry warning, alarm). On the contrary, if the contrast is reversed, the contact is not a fake fingerprint once printed on a film or the like, but it cannot be determined as a bioprint. This is because it may be a fake fingerprint made of a material such as silicone rubber. Therefore, in this case, the third light source 214 is operated by the light source control unit 220 to irradiate external light to the contact surface to check whether the imitation fingerprint is once again.

The reading method by comparing the images can be arbitrarily implemented by those skilled in the art of image processing or graphics processing. As an example, the sum of differences of gray levels in a predetermined area of each acquired image is calculated. If each image is inverted, the sum of the differences in the gray levels of the two will be very large. On the contrary, if the image is not inverted and is the same, the sum of the differences in the gray levels in a predetermined area will be almost the same (there may be some differences due to noise, but the difference due to noise is sufficiently processed by known image processing techniques. Available). Since this has been described in the foregoing description of the method of the present invention, it will not be described separately. In addition, it is possible to analyze the contrast of the contrast between the two images by various techniques at the discretion of those skilled in the art.

When the determination result that there is a contrast inversion between the first image and the second image from the first imitation fingerprint determiner 240 is transmitted to the main control unit 260, the main control unit 260 causes the light source control unit 220 to perform a third operation. The light source 214 is turned on and the system is controlled to instruct a third image to be acquired. The acquired third image is analyzed by the second imitation fingerprint determiner 250. Second imprint fingerprint determination unit (2500) From the contact surface image acquired by external light irradiation, that is, the gray level distribution of the third image, whether the third image has a gray level distribution corresponding to the biofingerprint. The main controller 260 finally determines whether the contact is a fake fingerprint or a biometric fingerprint to continue the fingerprint authentication process by analyzing whether the gray level distribution has a corresponding gray level distribution. A method of identifying whether the fingerprint is imitated by analyzing the distribution has been described above with reference to FIGS. 10 to 13.

On the other hand, in the fingerprint acquisition apparatus according to the present invention, since two light sources irradiating light to pass through the inside of the prism 200, that is, the first light source and the second light source 210 and 212, are used as shown in FIG. When the first image is acquired by the scattering equation, since the second light source 212 is positioned in the middle of the optical path of the first light source 210, even if the second light source 212 is turned off, the first light source 210 is turned off. A portion of the light emitted from the light emitted from the prism 200 is reflected by the second light source 212, the light 211 is re-incident to the prism 200 is present. (In order to prevent this, the scattering optics are actually coated with a black color on the third surface 206 of the prism 200.) Since this phenomenon degrades the quality of the scattered image, the correct operation is performed. This is a problem that must be solved, especially in the case of a system using a scattering image as an image for fingerprint authentication, because it is directly connected to the quality level of the fingerprint image.

To solve this problem, as shown in FIG. 16, a blocking plate 213 may be provided between the third surface 206 of the prism 200 and the second light source 212. However, in the present invention, since the image must be acquired by absorption, when the blocking plate 213 is installed, the second light source 212 cannot irradiate light into the prism 200. In order to achieve the object of the present invention, both the first light source 210 and the second light source 212 should be able to operate in one optical system (since the third light source 214 does not irradiate light into the prism) At the same time, each light source should not be affected by other light sources when it is operating. In consideration of this problem, the blocking plate 213 should be a plate that transmits light but has a low reflectance (for example, a dark diffusion plate or a black plate for observing sunspots). That is, when the first light source 210 is turned on, it has a dark color to give the same effect as black coating the entire surface of the third surface 206 of the prism 200, and when the second light source 212 is turned on, The light irradiated from the two light sources should be made of a light-transmissive material so as to be incident into the prism through the third surface 206 of the prism 200. Hereinafter, the blocking plate 213 will be referred to as a semi-reflective plate 213. The anti-reflective plate 213 may be diffused to treat the light of the second light source 212 on the entire surface of the third surface 206 of the prism 200. (In a diffuse fingerprint acquisition device, It is most preferable to use a surface light emitting source for irradiating the entire prism incidence surface. The semi-reflective plate 213 can be easily applied by those skilled in the art.

The configuration and operation of the imitation fingerprint identification method and apparatus according to the present invention has been described above. Specific embodiments of the present invention have been described with reference to the drawings. However, the technical scope of the method and apparatus for identifying a fake fingerprint of the present invention is not limited to the above specific embodiments, but is defined in the appended claims. It is determined by rational interpretation.

According to the present invention, even if the imitation fingerprint is produced in any form, it is possible to identify the imitation fingerprints of various forms in one system. In particular, since scattering and absorption image acquisition are performed in one optical system, imitation fingerprints printed on films and the like can be identified using relatively simple hardware and algorithms, and are conventionally misidentified by fingerprint marks (residual fingerprints) remaining in the fingerprint input window. Since the problem is similar to the imitation fingerprint in the form of a film, errors in fingerprint authentication due to the remaining fingerprint can be solved together. On the other hand, since the imitation fingerprint which can not be identified even by the scattering / absorption image acquisition can be identified by an external light irradiation method, security can be further enhanced by only adding a relatively simple algorithm in one system.

Claims (23)

A method of determining whether a contact is a biometric fingerprint or a fake fingerprint by acquiring an image of an object (hereinafter referred to as "contact body") in contact with the fingerprint input window of the fingerprint acquisition device, (1) The first image acquired by the optical scattering method for the contact placed in the fingerprint input window, the second image acquired by the optical absorption method for the contact, and the external light is transmitted so that the light passes along the inner side adjacent to the contact surface of the contact. Providing a surface image (third image) of the contact body, which is obtained by detecting the external light irradiated to the contact body after passing through the inside of the contact body and exiting out of the contact body; (2) In the above images, when the contrast between the first image and the second image is inverted or the gray level distribution of the third image is analyzed to have a gray level distribution corresponding to the bio fingerprint, the contact member may be If the fingerprint is determined to be a bio fingerprint, and the contrast between the first and second images is not reversed, or if the gray level distribution of the third image has a gray level distribution corresponding to the dummy fingerprint, the contact is a fake fingerprint. A fake fingerprint identification method comprising the step of determining. A method of determining whether a contact is a biometric fingerprint or a fake fingerprint by acquiring an image of an object (hereinafter referred to as "contact body") in contact with the fingerprint input window of the fingerprint acquisition device, (1) acquiring a first image by an optical scattering method for a contact placed on a fingerprint input window, and acquiring a second image by an optical absorption method for a contact, and comparing these images; (2) comparing the first and second images and determining that the contact is a fake fingerprint when the contrast of both images is not reversed; (3) When the contrast between the first image and the second image is inverted from each other, external light is irradiated to transmit light along the inner side adjacent to the contact surface of the contact body, Acquiring a surface image (third image) of the contact by detecting that light passes through the inside of the contact and then exits to the outside of the contact; (4) Analyzing the gray level distribution of the acquired third image, if the gray level distribution corresponding to the bio fingerprint is determined, the contact is a bio fingerprint, and the gray level distribution of the third image is gray corresponding to the dummy fingerprint. And if the contact has a level distribution, determining that the contact is a fake fingerprint. The method of claim 1 or 2, wherein the step of determining the contrast of the contrast by comparing the first image and the second image When the sum of the differences between the gray levels of the first and second images is larger than the reference value, it is determined that there is a contrast inversion between the two images. The counterfeit fingerprint identification method according to claim 1, wherein when the sum of the differences of gray levels in the predetermined areas of the first and second images is smaller than the reference value, the counterfeit fingerprint is judged to have no contrast inversion between the two images. The method of claim 1, wherein the analyzing of the gray level distribution of the third image comprises: Setting a plurality of sections in a direction away from the point where the external light is incident on the contact body (hereinafter, the incident position) in the gray level distribution chart for each distance of the third image; When the maximum value of the gray level in each of the set intervals is detected, and the maximum value of the detected gray level is far from the point at which external light starts to be incident, the maximum value of the gray level in each section decreases. Imitation fingerprint identification method comprising the step of determining with the fingerprint. The method of claim 1, wherein the analyzing of the gray level distribution of the third image comprises: Setting a plurality of sections in a direction away from an incident position where external light is incident on the contact in the gray level distribution chart for each distance of the third image; Setting a maximum reference range of the gray level for each of the set sections; Calculating a maximum value of the gray level for each of the set sections; And comparing the maximum value of the calculated gray level for each section with a predetermined reference range and determining that the fingerprint is a biometric fingerprint. The method of claim 1, wherein the analyzing of the gray level distribution of the third image comprises: Setting a plurality of sections in a direction away from an incident position where external light is incident on the contact in the gray level distribution chart for each distance of the third image; Setting an average value reference range of gray levels for each of the set sections; Calculating an average value of gray levels in each of the set sections; And comparing the average value of the calculated gray levels for each section with a predetermined reference range and determining that the fingerprint is a biofingerprint. The method of claim 1 or 2, wherein the light in the external light irradiation step is invisible light. The method of claim 4, further comprising: excluding a predetermined distance from the incident position. The method of claim 5, further comprising: excluding a predetermined distance from the incident position. 7. The method of claim 6, further comprising excluding a predetermined distance from the incident position. A system for acquiring an image of an object (hereinafter referred to as "contact body") in contact with a fingerprint input window of a fingerprint acquisition device and determining whether the contact body is a bio fingerprint or a fake fingerprint. A prism including a fingerprint input window and a fingerprint exit surface on which an image of the input fingerprint is output; A first light source installed at a position that emits light at an angle that is not totally reflected from the inner surface of the fingerprint input window of the prism to perform scattered fingerprint acquisition; A second light source installed at a position that emits light at an angle totally reflected from the inner surface of the fingerprint input window of the prism to perform absorption type fingerprint acquisition; A third light source irradiating external light to transmit light along an interior adjacent to a surface of the contact body contacting the fingerprint input window; A light source controller for selectively operating the first light source, the second light source, and the third light source; When the first light source is turned on by the light source control unit, a first image emitted from the fingerprint exit surface of the prism is detected, and when the second light source is turned on, a second image exited from the fingerprint exit surface of the prism is detected. An image detector detecting a surface image (third image) of the contact body in contact with the fingerprint input window of the prism when the third light source is turned on; Among the three images, among the three images, the contrast between the first image and the second image is inverted, or the gray level distribution corresponding to the bio fingerprint is analyzed by analyzing the gray level distribution of the third image. It is determined that the contact is a bio fingerprint, and if the contrast of both images is not reversed by comparing the first and second images, or if the gray level distribution of the third image has a gray level distribution corresponding to the dummy fingerprint, A counterfeit fingerprint identification device comprising a counterfeit fingerprint judge that determines that the contact is a counterfeit fingerprint. A system for acquiring an image of an object (hereinafter referred to as "contact body") in contact with a fingerprint input window of a fingerprint acquisition device and determining whether the contact body is a bio fingerprint or a fake fingerprint. A prism including a fingerprint input window and a fingerprint exit surface on which an image of the input fingerprint is output; A first light source installed at a position that emits light at an angle that is not totally reflected from the inner surface of the fingerprint input window of the prism to perform scattered fingerprint acquisition; A second light source installed at a position that emits light at an angle totally reflected from the inner surface of the fingerprint input window of the prism to perform absorption type fingerprint acquisition; A third light source irradiating external light to transmit light along an interior adjacent to a surface of the contact body contacting the fingerprint input window; A light source controller for selectively operating the first light source, the second light source, and the third light source; When the first light source is turned on by the light source control unit, a first image emitted from the fingerprint exit surface of the prism is detected, and when the second light source is turned on, a second image exited from the fingerprint exit surface of the prism is detected. An image detector detecting a surface image (third image) of the contact body in contact with the fingerprint input window of the prism when the third light source is turned on; A first imitation fingerprint determiner which processes the first image and the second image detected by the image detection unit and outputs a result of imitation fingerprint determination when the contrast between the two images is not inverted; In the case where the contrast of the first and second images is analyzed by the first imitation fingerprint determiner, whether the third image has a gray level distribution corresponding to the bio fingerprint from the gray level distribution of the third image. And a second imitation fingerprint determiner for analyzing whether the gray level distribution corresponds to the imitation fingerprint and outputting a determination result. The apparatus of claim 11 or 12, wherein the prism is a triangular prism. The method of claim 11, wherein the imitation fingerprint judgment unit Means for calculating a sum of differences of gray levels in a predetermined region of each image of the first image and the second image, If the sum of the gray level differences between the two images is larger than the reference value, it is determined that there is a contrast contrast between the two images. Imitation fingerprint identification device comprising a means for. The method of claim 11, wherein the imitation fingerprint judgment unit In the gray level distribution chart for each distance of the third image, the maximum value of the gray level in each section set in a direction away from the incident position at which external light is incident on the contact is detected. And a means for discriminating with a biometric fingerprint when the maximum value of the gray level for each section decreases as it moves away from the point where the incident starts. The method of claim 11, wherein the imitation fingerprint judgment unit Detecting the maximum value of the gray level in each section set in the direction away from the incident position where the external light is incident on the contact in the gray level distribution chart for each distance of the third image, and calculates the maximum value of the gray level for each set section And means for discriminating that the maximum value of the calculated gray level is a biofingerprint when it falls within the reference range by comparing with the set gray level maximum value reference range. The method of claim 11, wherein the imitation fingerprint judgment unit In the gray level distribution chart for each distance of the third image, the maximum value of the gray levels in each section set in a direction away from the incident position where external light is incident on the contact is detected, and the average value of the gray levels in each set section is calculated. And means for discriminating that the average value of the calculated gray levels is a biofingerprint when compared with the set gray level average value reference range and included in the reference range. The method of claim 12, wherein the first imitation fingerprint judgment unit Means for calculating a sum of differences of gray levels in a predetermined region of each image of the first image and the second image, If the sum of the gray level differences between the two images is larger than the reference value, it is determined that there is a contrast contrast between the two images. Imitation fingerprint identification device comprising a means for. The method of claim 12, wherein the second imitation fingerprint judgment unit In the gray level distribution chart for each distance of the third image, the maximum value of the gray level in each section set in the direction away from the incident position where external light is incident on the contact is detected. And a means for discriminating with a biometric fingerprint when the maximum value of the gray level for each section decreases as it moves away from the point where the incident starts. The method of claim 12, wherein the second imitation fingerprint judgment unit Detecting the maximum value of the gray level in each section set in the direction away from the incident position where the external light is incident on the contact in the gray level distribution chart for each distance of the third image, and calculates the maximum value of the gray level for each set section And means for discriminating that the maximum value of the calculated gray level is a biofingerprint when it falls within the reference range by comparing with the set gray level maximum value reference range. The method of claim 12, wherein the second imitation fingerprint judgment unit In the gray level distribution chart for each distance of the third image, the maximum value of the gray levels in each section set in a direction away from the incident position where external light is incident on the contact is detected, and the average value of the gray levels in each set section is calculated. And means for discriminating that the average value of the calculated gray levels is a biofingerprint when compared with the set gray level average value reference range and included in the reference range. The method according to claim 11 or 12, wherein in the path where the light of the second light source enters into the prism, the light from the inside of the prism is not reflected and the light of the second light source is added to the inside of the prism. Imitation fingerprint identification device comprising a. 23. The apparatus of claim 22, wherein the antireflective film is subjected to a diffuser plate treatment so that light from the second light source is diffused and incident on the prism.

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