KR100874688B1 - Imitation Fingerprint Judgment Device and Judgment Method to Determine Imitation Fingerprint - Google Patents

Abstract

A counterfeit fingerprint judging apparatus capable of discriminating a counterfeit fingerprint and a method of determining the same are disclosed. The imitation fingerprint judgment of the present invention uses a different critical angle for total reflection when the imitation fingerprint contacts the fingerprint contact surface of the prism, and uses a fingerprint image obtained by using a separate light source whose optical axis of the emitted light has an incidence angle within a predetermined range. By comparison, it is determined whether it is a fake fingerprint.

Description

Apparatus for Distinguishing Forged Fingerprint and Method therof}

1 is a fingerprint image obtained through a conventional fingerprint recognition device,

2 is a block diagram of an optical fingerprint recognition device having a fake fingerprint determination device of the present invention;

3 is a view provided for the description of the fake fingerprint determination method;

4 is a view showing an image obtained using the biodetection light source of FIG.

5 is a view for explaining an example of the imitation fingerprint determination method of the present invention, and

6 is a view for explaining another example of the imitation fingerprint determination method of the present invention.

The present invention relates to an apparatus for judging fingerprints for fingerprint recognition and a method of judging the same, and more particularly, to an apparatus for judging fingerprints and a method for judging a fake fingerprint such as paper or film and a human bio fingerprint. will be.

The use of user biometric information with invariability and uniqueness for personal authentication using information devices has already been generalized. Among them, fingerprint recognition has become the most noticeable and generalized authentication means compared to other means due to its superior performance compared to a simple structure.

Normal personal authentication is mainly used in areas where security is important, such as access control, e-commerce, financial transactions, security of personal computers (PCs), and office payment systems. The most important thing is to effectively distinguish fingerprints (hereinafter referred to as 'fake fingerprints').

One method of making a fake fingerprint is to contact a fingerprint reader with a liquid or a liquid such as water or oil on a paper or film on which a fingerprint image is printed. A typical fingerprint recognition device recognizes such fake fingerprints and performs false authentication.

1 is a fingerprint image obtained through a conventional fingerprint recognition device, Figure 1 (a) is a biometric fingerprint, (b) is an image obtained from the imitation fingerprint described above. It can be seen that the two images are very similar.

In addition, when the user attaches such a fingerprint to a finger, the fingerprint is distinguished by imitation fingerprint identification techniques such as a temperature measurement method, a potential measurement method, a pressure measurement method, a blood flow measurement method, and a sweat gland measurement method. Hard.

Disclosure of the Invention An object of the present invention is to provide a counterfeit fingerprint judging device capable of discriminating a counterfeit fingerprint and a human biometric fingerprint and a method of determining the same.

In order to achieve the above object, according to the present invention, an imitation fingerprint determination method of acquiring a fingerprint image of an object in contact with a fingerprint contact surface and determining whether the object is a biometric fingerprint or an imitation fingerprint is performed. Irradiating a fingerprint contact surface, wherein the predetermined angle of incidence is an angle larger than a first critical angle for total reflection when the refractive index of the object is 1 and smaller than a second critical angle for total reflection when transparent liquid contacts the fingerprint contact surface; Acquiring a fingerprint image of the object formed by the irradiated light, calculating an area of the acquired fingerprint image, and determining the object as a biofingerprint when the calculated area of the fingerprint image is larger than a reference area; When it is small, it includes the step of judging the imitation fingerprint.

In the calculating of the area, the area of the fingerprint image may be obtained by obtaining the number of pixels having a gray level of a predetermined reference value or more in the entire image including the acquired fingerprint image.

In addition to the method of determining the area of the obtained fingerprint image to determine whether the imitation fingerprint is present, first, the average gray level of the entire image including the acquired fingerprint image or a predetermined portion of the entire image is calculated, and the calculated average gray is obtained. When the level is larger than the reference value, the object may be determined as a bio fingerprint, and when the level is smaller, the object may be determined as a fake fingerprint.

The second critical angle may be a critical angle when the transparent liquid is water, and the predetermined incident angle is preferably an intermediate angle between the first critical angle and the second critical angle.

An imitation fingerprint determination apparatus according to another embodiment of the present invention includes a light refraction device, a light source for determining a living body, an optical lens, an image sensor, and an imitation fingerprint determination unit.

The optical refractor includes a fingerprint contact surface to which an object for fingerprint image acquisition contacts and an emission surface to which the image of the fingerprint is emitted.

The biological judgment light source is provided such that an optical axis of the emitted light has a predetermined angle of incidence with respect to the fingerprint contact surface and emits the light to the fingerprint contact window. The predetermined angle of incidence is an angle greater than a first critical angle for total reflection when the refractive index of the object is 1 and smaller than a second critical angle for total reflection when a transparent liquid contacts the fingerprint contact surface.

The optical lens may be provided adjacent to the emission surface to form a fingerprint image emitted from the optical refraction machine, and the image sensor acquires a fingerprint image formed on the optical lens.

The imitation fingerprint judging unit calculates the area of the fingerprint image acquired by the image sensor, and when the calculated area of the fingerprint image is larger than the reference area, determines the object as a bio fingerprint, and when it is small, determines the imitation fingerprint.

Hereinafter, the present invention will be described in detail with reference to the drawings.

2 is a block diagram of an optical fingerprint recognition device having a fake fingerprint determination device of the present invention. The fingerprint recognition device 200 of FIG. 2 is implemented to include the fake fingerprint determination device of the present invention.

Referring to FIG. 2, the fingerprint recognition device 200 may include a prism 210, an internal light source 231 for irradiating a fingerprint recognition light source toward the prism 210, an optical lens 233 for imaging image information of a fingerprint, The image sensor 235, the controller 250, and the biodetection light source 270 are included.

The prism 210 includes a fingerprint contact surface 210a through which a fingerprint is contacted and an emission surface 210b through which light (fingerprint image) reflected or scattered from the fingerprint contact surface 210a is emitted. As shown in FIG. 2, the prism 210 not only has four sides (or a trapezoid) in its cross-sectional shape (or a shape other than an optically unused surface), but also has a three-sided shape (triangle) In addition to the prism, a broad concept of optical refractor can be used.

First, the basic fingerprint recognition process of the optical fingerprint recognition device 100 of FIG. 2 is as follows. When the user touches the finger on the fingerprint contact surface 210a, the light irradiated from the internal light source 231 is imaged on the optical lens 233 while passing through the fingerprint contact surface 210a and the exit surface 210b of the prism 210. It is input to the image sensor 235. In the scattered fingerprint recognition device 200 as shown in FIG. 2, the light emitted from the internal light source 231 is incident on the fingerprint contact surface 210a at an angle smaller than the critical angle for perpendicular or total reflection. The light emitted from the internal light source 231 passes or scatters along the valleys and ridges of the fingerprint in contact with the fingerprint contact surface 210a to form a fingerprint image. The image sensor 235 obtains an image of the fingerprint in contact with the fingerprint contact surface 210a by outputting a digital fingerprint image signal, which is an electrical signal corresponding to the incident fingerprint image.

However, since the imitation fingerprint judgment of the present invention is implemented by another distinct mechanism different from the fingerprint recognition mechanism, the fingerprint recognition device 200 applied to the present invention is not limited to the scattering expression shown in FIG. 2. Therefore, as described above, the prism 210 is not limited in its cross-sectional shape, such as trapezoid or triangle, and the position of the internal light source 231 is provided at various positions according to the fingerprint recognition method and the shape of the prism 210. Can be.

The controller 250 controls the overall operation of the fingerprint recognition device 200 including acquiring a fingerprint image.

In addition, the controller 250 includes a fake fingerprint determination unit 251 to determine whether the fingerprint contacted to the fingerprint contact surface 210a is a biometric fingerprint or a fake fingerprint.

After the imitation fingerprint determination unit 251 turns on the biodetection light source 270, the fingerprint contact surface based on the digital fingerprint image signal input from the image sensor 235 through the prism 210 and the optical lens 233. It is determined whether the fingerprint in contact with 210a is a fake fingerprint. At this time, the internal light source 231 is controlled to be in an off state.

The biodetection light source 270 irradiates light for distinguishing the imitation fingerprint to the fingerprint contact surface 210a. The biological determination light source 270 preferably uses a light source having a predetermined viewing angle (for example, about 30 °) around the optical axis of the light source.

The light emitted from the biopsy light source 270 to the fingerprint contact surface 210a is totally reflected, absorbed or refracted, and is then imaged on the optical lens 233 through the exit surface and input to the image sensor 235.

At this time, when the incident angle of the optical axis irradiated from the biometric light source 270 to the fingerprint contact surface 210a is within a predetermined range, the amount of light incident on the image sensor 235 is in contact with the fingerprint contact surface 210a ( Biometric fingerprint or imitation fingerprint). In other words, the area of the image acquired by the image sensor 235 using the biometric light source 270 varies according to the type of the fingerprint in contact with the fingerprint contact surface 210a. The operation of the biometric light source 270 and the determination of the dummy fingerprint will be described again below.

In the above, the fingerprint recognition device 200 of FIG. 2 is implemented to use the prism 210, the optical lens 233, and the image sensor 235 in common for acquiring a fingerprint image and determining a fake fingerprint. However, according to the difference in the fingerprint recognition method, the fingerprint recognition device 200 may be provided with a separate optical lens and an image sensor for obtaining a fingerprint image using the biometric light source 270.

In addition, according to another embodiment, it may be implemented as an independent imitation fingerprint device that does not include the internal light source 231 and determines only whether the fingerprint contacted to the fingerprint contact surface 210a is a bio fingerprint or a fake fingerprint.

Hereinafter, a method of determining the imitation fingerprint using the biopsy light source 270 will be described in more detail.

3 is a view provided to explain the method of determining the imitation fingerprint.

When the refractive index of the prism 210 is n ₁ and the refractive index of the medium in contact with the fingerprint contact surface 210a of the prism 210 is n ₂ , the imitation fingerprint determination method of the present invention contacts the fingerprint contact surface 210a. The critical angle for total reflection at the fingerprint contact surface 210a varies depending on the type of fingerprint (bioprint or fake fingerprint).

When light is irradiated from a medium having a large refractive index to a medium having a small refractive index, the incident light is refracted if the incident angle is less than or equal to the critical angle, and totally reflected if it is greater than or equal to the critical angle. The critical angle is determined by the refractive indices of the two media forming the interface.

3A illustrates a case where there is no contact with the fingerprint contact surface 210a, and the refractive index n ₂ is 1, which is the refractive index of air. In addition, hereinafter, it is assumed that the refractive index n ₁ of the prism 210 is 1.6 for convenience of explanation.

Snell's law for calculating the critical angle for total reflection is as shown in Equation 1 below.

Here, θ ₁ is the angle of incidence and θ ₂ is the angle of refraction. Θ ₂ for total reflection is 90 °.

When n ₁ = 1.6, n ₂ = 1 (refractive index of air) and θ ₂ = 90 ° are applied to Equation 1, a critical angle for total reflection when there is no contact with the fingerprint contact surface 210a (hereinafter, referred to as 'first critical angle') Θ _min is obtained as follows.

1.6 × sinθ _min = 1.0 × sin90 °

θ _min = sin ^-1 (1 / 1.6) ≒ 39 °

Therefore, when the incident angle θ _i of the light irradiated from the biometric light source 270 to the fingerprint contact surface is smaller than the first critical angle θ _min , the amount of light refracted by the fingerprint contact surface 210a and incident on the image sensor 235 is remarkably given. When the incident angle θ _i is greater than the first critical angle θ _min , most of the light emitted from the biopsy light source 270 is totally reflected at the fingerprint contact surface 210a to reach the image sensor 235.

3B illustrates a case where the dummy fingerprint 310 contacts the fingerprint contact surface 210a. Here, the imitation fingerprint 310 is soaked or soaked in a transparent liquid such as water or oil on the paper or film (Film) on which the fingerprint image is printed. Hereinafter, assuming that the transparent liquid is water (refractive index 1.33), the critical angle (hereinafter referred to as 'second critical angle') θ _max for total reflection when the dummy fingerprint 310 is contacted is obtained as follows.

1.6 × sinθ _max = 1.33 × sin90 °

θ _max = sin ^-1 (1.33 / 1.6) ≒ 56 °

Therefore, when the incident angle θ _i of the light irradiated from the biodetection light source 270 to the fingerprint contact surface is smaller than the second critical angle θ _max , the incident angle θ _i is refracted by the fingerprint contact surface 210 a, and when the incident angle θ _i is larger than the second critical angle θ _max , the fingerprint contact surface is present. Total reflection at 210a reaches the image sensor 235.

At this time, since the transparent liquid constituting the imitation fingerprint is in contact with most of the fingerprint contact surface 210a, the optical characteristics caused by the imitation fingerprint are ignored and are optically identical by the liquid. As a result, the light incident at the incident angle θ _i smaller than the second critical angle θ _max is mostly refracted, and the amount of light incident on the image sensor 235 is very small.

The second critical angle with respect to the determination of θ _max, based on the low-refractive index of the transparent liquid (water, alcohols, etc.) that can be used in the artificial fingerprint is preferable to set the second critical angle θ _max. It is desirable to base the water on its refractive index, which is smaller than other liquids, and is usually the simplest and most commonly used.

Based on the above description, the case where the incident angle θ _i of the light emitted from the biopsy light source 270 is set as in Equation 2 below will be described.

Based on these conditions, in the case of the biofingerprint, total reflection may occur in the bone on the fingerprint, whereas in the case of the imitation fingerprint, the possibility of total reflection is significantly reduced, so that the amount of light incident on the image sensor 235 is input to the biofingerprint and the imitation fingerprint. Depends on. Therefore, based on Equation 2, it is possible to distinguish whether the fingerprint in contact with the fingerprint contact surface 210a is a biometric fingerprint or a fake fingerprint.

Here, since the incident angle θ _i refers to the incident angle formed by the optical axis of the light emitted from the biodetection light source 270 to the fingerprint contact surface 210a, the incident angle θ _i of the light emitted from the biodetection light source 270 is used for the biological judgment. The attitude of the light source 270 is determined. That is, the angle of incidence formed by the optical axis of the light emitted from the biopsy light source 270 should be provided so as to satisfy Equation 2 above. However, there is no limitation on the point where the optical axis of the biopsy light source 270 meets the fingerprint contact surface 210a, but the center of the fingerprint contact surface 210a is preferable.

Referring to FIG. 2, the biological judgment light source 270 is provided to irradiate light for distinguishing a fingerprint from the fingerprint contact surface 210a, and the incident angle formed by the optical axis of the light emitted from the biological judgment light source 270 is determined. It is provided so as to satisfy the expression (2).

Therefore, when using the imitation fingerprint 310 soaked in water, the incident angle of the biopsy light source 270 may be 39 ° ≤ θ _i ≤ 56 °, it is most preferable to set the middle angle of 48 ° Do.

FIG. 4 is a diagram illustrating an image acquired by using the biodetection light source, and includes a fingerprint image as a whole image received from the image sensor 235 using the biodetection light source 270. Hereinafter, with reference to FIGS. 2 and 4, when the light emitted from the biodetection light source 270 is incident on the fingerprint contact surface 210a at an incident angle of 48 °, an image obtained by the image sensor 235 will be described.

When the bio fingerprint is in contact with the fingerprint contact surface (210a), the path of the light emitted from the bio-judgment light source 270 depends on the bone and ridge of the bio fingerprint. Since the part where the bone of the biofingerprint is in contact does not have any contact (first critical angle θ _min ), the incident angle of the light emitted from the biological judgment light source 270 is greater than the first critical angle θ _min so that the total reflection Occurs. Light irradiated to the contact area of the ridge of the bio fingerprint is absorbed or scattered.

However, since a general light source is emitted with a viewing angle of about 30 ° with respect to the optical axis, total reflection is not all performed at the contact surface of the bone of the fingerprint. Therefore, the image acquired by the image sensor 235 may not be a fingerprint image that can be properly recognized, and FIG. 4A is an example.

When the dummy fingerprint is in contact with the fingerprint contact surface 210a, the critical angle applied to the fingerprint contact surface becomes the second critical angle θ _max . Since the incident angle of the light emitted from the biopsy light source 270 is smaller than the second critical angle θ _max , refraction occurs throughout the fingerprint contact surface 210a. Therefore, the amount of light incident on the image sensor 235 becomes very small, and the image obtained by the image sensor 235 is as shown in FIG.

Comparing (a) and (b) of Figure 4, it can be seen that the area of the portion (black portion) where the fingerprint image is obtained is significantly different. The images of (a) and (b) are inverted of the entire image received from the image sensor 235. In fact, the fingerprint image incident on the optical lens 233 and the image sensor 235 corresponds to the part where the actual light is incident, and thus appears brighter than other parts.

The fingerprint recognition device 200 determines whether the fingerprint contacted to the fingerprint contact surface 210a is a fake fingerprint or a bioprint based on the fingerprint image.

Hereinafter, a method for determining whether the fingerprint is imitation using the image of FIG. 4 will be described based on the operation of the imitation fingerprint determination unit 251.

On the basis of the image inputted from the image sensor 235 by the imitation fingerprint determining unit 251, a method of determining whether the fingerprint contacted to the fingerprint contact surface 210a is a imitation fingerprint is the size of the acquired fingerprint image (or Information derived corresponding to size).

As an example, since the area of the fingerprint image acquired by the image sensor 235 is different for the biometric fingerprint and the dummy fingerprint, there is a method of determining that the fingerprint is a fake fingerprint when the area of the acquired fingerprint image is smaller than a predetermined reference area.

5 is a view for explaining an example of the fake fingerprint determination method of the present invention.

The imitation fingerprint determination unit 251 outputs a predetermined control signal when the fingerprint is in contact with the fingerprint contact surface 210a so that the biodetection light source 270 is turned on (S501) and then the fingerprint image through the image sensor 235. The entire image including the input is received (S503).

The imitation fingerprint determination unit 251 calculates the area of the fingerprint image among the entire images. The calculation of the area may be performed by obtaining a number of pixels whose gray level of the pixel is larger than a threshold level (which may be different from the previous reference level and determining whether there is an image). S505).

The imitation fingerprint determination unit 251 determines whether the area of the fingerprint image calculated in step S505 is larger than the reference area. Here, the reference area corresponds to a value for distinguishing the area of the fingerprint image at the time of the biometric fingerprint from the area of the fingerprint image at the time of imitation fingerprint based on FIG. 4, and can be obtained experimentally (S507).

As a result of the determination in step S507, the imitation fingerprint determination unit 251 determines that the fingerprint is biometric fingerprint if the area of the fingerprint image is larger than the reference area (S509), and if it is smaller than the reference area (S511).

According to an embodiment, the imitation fingerprint determination unit 251 determines whether the fingerprint image acquired in the range of the predetermined area (the area range of the fingerprint image corresponding to the biometric fingerprint) corresponds to the determination method of steps S507 to S511. You can also determine whether the fingerprint is fake.

The difference in the area of the acquired fingerprint image corresponds to the difference in the average gray level obtained for the entire image or a portion of the entire image. Therefore, there is a method of determining the gray level of the entire image (or a portion thereof) input from the image sensor 235 and determining the fake fingerprint when the gray level is smaller than the reference level.

In the case of obtaining the average gray level for a part of the entire image, it is preferable to apply an area (for example, A of FIG. 4) larger than the normal area of the fingerprint image obtained by an imitation fingerprint obtained experimentally.

However, depending on whether the entire image inputted from the image sensor 235 is inverted, a fingerprint image having an average gray level larger than the reference level may be determined as a fake fingerprint.

6 is a view for explaining another example of the imitation fingerprint determination method of the present invention.

The imitation fingerprint determination unit 251 outputs a predetermined control signal when the fingerprint is in contact with the fingerprint contact surface 210a so that the biodetection light source 270 is turned on (S601), and then the fingerprint image through the image sensor 235. The entire image including the input is received (S603).

The imitation fingerprint determining unit 251 calculates an average gray level of a predetermined portion (eg, A of FIG. 4) of the entire image (S605), and compares the calculated average gray level with a reference value (S607).

As a result of the comparison in step S607, the imitation fingerprint determination unit 251 determines that the average gray level is larger than the reference value as a biometric fingerprint (S609), and when the average fingerprint level is smaller than the reference value (S611).

In the above manner, the fake fingerprint determination unit 251 may determine whether the obtained fingerprint image is due to the fake fingerprint.

The invention can be implemented in methods, devices and systems. In addition, when the present invention is implemented in computer software, the components of the present invention may be replaced with code segments necessary for performing necessary operations. The program or code segment may be stored in a medium that can be processed by a microprocessor and transmitted as computer data coupled with carrier waves via a transmission medium or communication network.

The media that can be processed by the microprocessor include electronic circuits, semiconductor memory devices, ROMs, flash memory, electrically erasable programmable read-only memory (EEPROM), floppy disks, optical disks, and hard disks. (Hard) Includes the ability to transmit and store information such as disks, fiber optics, wireless networks, and the like. Computer data also includes data that can be transmitted over electrical network channels, optical fibers, electromagnetic fields, wireless networks, and the like.

In addition, although the preferred embodiment of the present invention has been shown and described above, the present invention is not limited to the above-described specific embodiment, the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Of course, various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or the prospect of the present invention.

As described in detail above, the apparatus for determining a fake fingerprint according to the present invention can easily and effectively determine whether the counterfeit fingerprint is a forged fingerprint.

The imitation fingerprint determination method of the present invention is particularly excellent for imitation fingerprints made by soaking paper or film on which a fingerprint image is printed in a transparent liquid.

Claims (10)

In the imitation fingerprint determination method of acquiring a fingerprint image of an object in contact with the fingerprint contact surface to determine whether the object is a bio fingerprint or a fake fingerprint, The optical axis is irradiated with light having a predetermined angle of incidence to the fingerprint contact surface, wherein the predetermined angle of incidence is greater than the first critical angle for total reflection when the refractive index of the object is 1, and total reflection when transparent liquid contacts the fingerprint contact surface. Stamping smaller than the second critical angle for; Acquiring a fingerprint image of the object formed by the irradiated light; Calculating an area of the acquired fingerprint image; And And determining the object as a biological fingerprint when the area of the calculated fingerprint image is larger than a reference area, and determining as an imitation fingerprint when the calculated fingerprint image is larger than the reference area. The method of claim 1, The step of calculating the area, And determining the area of the fingerprint image by obtaining the number of pixels having a gray level equal to or greater than a predetermined reference value in the entire image including the acquired fingerprint image. In the imitation fingerprint determination method of acquiring a fingerprint image of an object in contact with the fingerprint contact surface to determine whether the object is a bio fingerprint or a fake fingerprint, The optical axis is irradiated with light having a predetermined angle of incidence to the fingerprint contact surface, wherein the predetermined angle of incidence is greater than the first critical angle for total reflection when the refractive index of the object is 1, and total reflection when transparent liquid contacts the fingerprint contact surface. Stamping smaller than the second critical angle for; Acquiring a fingerprint image of the object formed by the irradiated light; Calculating an average gray level of the entire image including the acquired fingerprint image or a predetermined portion of the whole image; And And determining the object as a bio fingerprint when the calculated average gray level is larger than a reference value, and determining as an imitation fingerprint when the calculated average gray level is smaller than the reference value. The method according to claim 1 or 3, And the second threshold angle corresponds to a case where the transparent liquid is water. The method according to claim 1 or 3, And the predetermined incident angle is an intermediate angle between the first critical angle and the second critical angle. An optical refractor including a fingerprint contact surface to which an object for fingerprint image acquisition contacts and an emission surface to which the image of the fingerprint is emitted; The optical axis of the emitted light is provided to have a predetermined angle of incidence with respect to the fingerprint contact surface, and the light is emitted to the fingerprint contact window, wherein the predetermined angle of incidence is greater than a first critical angle for total reflection when the refractive index of the object is 1. A biometric light source having an angle smaller than the second critical angle for total reflection when a transparent liquid contacts the fingerprint contact surface; At least one optical lens provided adjacent to the exit surface to form a fingerprint image output from the optical refraction device; An image sensor which acquires a fingerprint image formed on the optical lens; And A fake fingerprint judgment unit that calculates an area of the fingerprint image acquired by the image sensor and determines the object as a bio fingerprint when the calculated fingerprint image area is larger than a reference area, and determines that the fingerprint is a fake fingerprint when the image is smaller than the reference area; Imitation fingerprint judgment device, characterized in that. The method of claim 6, The imitation fingerprint judgment portion, And an area of the fingerprint image is obtained by obtaining the number of pixels having a gray level of a predetermined reference value or more in the entire image including the acquired fingerprint image. An optical refractor including a fingerprint contact surface to which an object for fingerprint image acquisition contacts and an emission surface to which the image of the fingerprint is emitted; The optical axis of the emitted light is provided to have a predetermined angle of incidence with respect to the fingerprint contact surface, and the light is emitted to the fingerprint contact window, wherein the predetermined angle of incidence is greater than a first critical angle for total reflection when the refractive index of the object is 1. A biometric light source having an angle smaller than the second critical angle for total reflection when a transparent liquid contacts the fingerprint contact surface; At least one optical lens provided adjacent to the exit surface to form a fingerprint image output from the optical refraction device; An image sensor which acquires a fingerprint image formed on the optical lens; And The average gray level of the entire image including the fingerprint image acquired by the image sensor or a predetermined portion of the entire image is calculated, and when the calculated average gray level is larger than the reference value, the object is determined as a biofingerprint, When the imitation fingerprint judging unit judging as a fake fingerprint; imitation fingerprint determination apparatus comprising a. The method according to claim 6 or 8, And the second critical angle corresponds to a case where the transparent liquid is water. The method according to claim 6 or 8, And the predetermined incident angle is an intermediate angle between the first critical angle and the second critical angle.

Images