EP3782136B1 - Method for the verification of a luminescent-material-based security feature - Google Patents

Description

The present invention relates to a method for verifying a security feature.

It has long been known from the prior art to provide security documents with security features in the form of luminescent substances in order to make them forgery-proof or verifiable. Such security features must be verified using suitable procedures.

From the WO 2012/083469 A1 a device for the authentication of documents marked with photochromic systems is known. The photochromic security feature shows a color change and/or a change in shape under the action of a flash light excitation. It is also described that the security feature is based on a retinal protein.

The DE 10 2011 082 174 A1 and the WO 2013/034471 A1 describe an apparatus for recognizing a document having a security feature with wavelength conversion properties. For this purpose, a light generating device is provided, which irradiates the security feature with excitation light, and an image recording device, which records the light emitted by the security feature.

The WO 2013/034603 A1 describes a method for verifying a security document with a security feature in the form of a fluorescent printing element. The method provides that the printing element is excited by means of a light source and it is thereby exposed to electromagnetic radiation emitted, which is detected in a further step by means of a sensor. The recorded data is evaluated by comparing it with specified data. In a further step, the verification result is output depending on the result of the comparison. In particular, the method is to be carried out with a smartphone, the flash module of the smartphone being used as the excitation source and the photo sensor of the camera of the smartphone being used as the detection unit.

From the US 2010/0144387 A1 a multifunctional transportable device is known. The device includes a camera module, a processor unit and a display.

RADKE, RJ et al: "Image change detection algorithms: a systematic survey", IEEE TRANSACTIONS ON IMAGE PROCESS, Vol. 14, No. 3, 2005-03-01, pages 294-307, ISSN: 1057-7149 , describes algorithms for detecting image changes when viewing multiple images of the same subject at different points in time. Among other things, the alignment of the images and the determination of the image difference are explained.

DE 10 2011 121 566 A1 shows a method for assisting a user in checking the authenticity of a bank note. A portable data processing system with a camera and a screen is used. The data processing system uses a recorded image to check a security feature of the bank note.

U.S. 2007/090190 A1 shows a code reader for displaying an image that was recorded by a camera. Furthermore, the code reader is used to extract a code image from the image and to decode a code contained in the code image.

From the EP 1 295 263 A1 a method for authenticating an object with a security feature is known. The security feature includes physical or logical security elements, which can be excited by energy using a mobile device and can also be detected.

The DE 20 2016 002 731 U1 describes a device for a portable smart device with a camera, the device being a case. The case features a slot where the smart device is positioned so that the camera is also aligned. The device also includes a UV and/or blue light illumination unit for illuminating an object to be authenticated. The device also includes a positioning device for positioning the device relative to the object to be authenticated.

In the verification of the luminescent-based security features described in the aforementioned prior art, two hitherto unsolved problems have emerged. Previously known phosphors are regularly used as so-called conversion phosphors for the production of white LEDs, so that these phosphors are also regularly contained in the flashing LEDs of the image recording units (cameras) of smartphones and similar mobile devices. If one wishes to use such devices to provide the excitation radiation for checking security features, then the excitation source shows the same emissions as from the one to be examined Security feature are expected, so that a secure verification is excluded. A second problem results from the fact that the phosphors mentioned in the prior art have very short decay times in the ns to μs range. Since the camera of a mobile device typically has a relatively low recording speed (modern premium smartphones up to 240 fps), the emissions originating from the security feature are regularly already high when triggered by a smartphone flash decayed before the picture can be taken with the camera of a smartphone after the end of the excitation.

According to the state of knowledge prior to the invention, experts assumed that luminescent-based security features are hardly suitable for verification that is easy to carry out under everyday conditions and at the same time meets comparatively high security requirements, since they cannot be verified with inexpensive and widely used devices. Either the well-known security features require very special testing devices that can only be provided by larger units such as banks or passport control offices. Or the security features that can be checked with generally available devices such as smartphones in particular are easy to forge.

It is therefore an object of the present invention to provide an improved method for verifying a luminescent-based security feature. In particular, the security feature should be able to be detected by means of an image recording unit of a smartphone and also be verifiable with the data processing unit of the smartphone. In particular, not only the presence of an emission but specific properties of the emission should be checked during verification.

According to the invention, the object is achieved by a method for verifying a luminescent-based security feature according to appended claim 1.

A general solution idea for the stated task, which the invention implements, is that a security feature with a specific phosphor is equipped that circumvents the problems described above. For this purpose, this phosphor must be configured in such a way that it can be excited with a light source of a smartphone or a similar mobile data processing device, ie in particular a flashing LED of a smartphone. At the same time, the phosphor must have such a luminescence characteristic (luminescence yield, decay time) that it is still possible to reliably detect the decaying luminescence signals even after the end of the flash light excitation. The decay time and the emission occurring during the decay must be distinguishable from other phosphors and, in addition, the decaying luminescence signals should not be visually perceptible to humans. It has been shown that these conditions are only met by a few specifically configured phosphors that can be used in security features. Such a phosphor must in particular have a decay time in the ms range. A suitable phosphor is in the German patent application DE 10 2018 109 141.9 entitled "Smartphone verifiable luminescent-based security feature and arrangement for verification" filed by the applicant with the same priority date (04/17/2017). The content of this further patent application, in particular with regard to the composition and the production of a phosphor that can be used here, is expressly and completely included in the disclosure of the present invention.

The method according to the invention serves to verify a luminescent-based security feature that can be stimulated to emit and is arranged on a security document. The method can be carried out using a smartphone or a similar mobile device, which is Software, preferably configured and controlled in the manner of an app.

A security feature that can be evaluated by the method according to the invention is applied to a security document or introduced into it and includes the above-mentioned phosphor. The phosphor can be excited to luminescence with electromagnetic radiation of a predetermined wavelength, whereupon it emits radiation. The emission of the phosphor has a decay time in the ms range. The decay time is preferably selected in the range between 1 and 100 ms, particularly preferably in the range between 5 and 50 ms, again preferably between 10 and 30 ms. Furthermore, the emission of the phosphor can be detected by means of an image acquisition unit of a smartphone.

In a first method step, the security document is positioned in such a way that the security feature is captured by an image recording unit of the smartphone. In the simplest case, this is done by manually positioning the security document in front of the image capture unit. A semi-transparent mask or a position frame is preferably shown in the display of the mobile terminal as user support, which serves as a position aid. An identifier which can be visually perceived by a human being and which is positioned within the positioning frame can be attached to the security document. The security feature is then attached in the vicinity of this identifier so that it is within the detection range of the image detection unit.

Alternatively, object recognition can be carried out using the image acquisition unit and a data processing unit of the smartphone (mobile terminal device). The object recognition indirectly serves to determine the position of the security feature on the document and/or it supports the positioning of the smartphone over the security document. Object detection can also be used to automatically trigger detection.

In an optional method step, a recording frame or a recording window is defined, its position being defined using the previously determined position of the security feature and the recording frame being selected such that the security feature is arranged in the area of the recording frame.

In a subsequent method step, the security feature is excited to luminescence by means of an illumination unit of the smartphone (mobile terminal device), so that the security feature emits electromagnetic radiation. The lighting unit and image recording unit are controlled by the data processing unit of the smartphone using an app (software application), with a combination of single flash and video recording or single flash and series recording taking place and with the lighting unit being switched off after the phosphor of the security feature has been activated, so that the decaying emission can be recorded by the image recording unit after the flash has ended.

An optional method step provides that a reference area is defined, which is located directly adjacent to the security feature. The evaluation of captured images of the security feature and the reference area as well as the differences captured there (image difference, histograms, Hue values) can be helpful for verifying the document in the case of heavily flickering extraneous light.

In a further method step, a series of images or a video of the security feature and optionally of the reference area is recorded using an image recording unit of the smartphone in order to record the emission. The recording preferably takes place in the defined recording area. The emission is recorded after the excitation has ended, ie after the flashlight has been switched off. The recording time of the series of images or the video recorded by the image acquisition unit is preferably selected such that emission of the security feature can no longer be detected in the last image of the series of images or the video, provided the predetermined decay times of the phosphor of the security feature are observed. This last image is recorded as a reference image (B _ref ). A start image can also optionally be recorded before the phosphor is excited, which can be included in the verification as a further reference.

In a further method step, the captured or recorded series of images or videos are processed by the data processing unit and compared with specification or reference data. In the simplest case, reference data are stored in the smartphone, which are compared with the determined emission parameters.

The image differences between the captured images and the reference image captured after the emission has decayed are preferably generated (Δ _1R -B ₁ -B _ref ... Δ _nR -B _n -B _ref ), from which the emission values are then calculated as the hue value of the different color channels using an RGB histogram, and then the decay time of the phosphor is calculated the determined data is analyzed. Preferably, n=10 images are used to calculate the image difference. The number of images is preferably between 5 and 15 images.

wobei Δt das Zeitintervall zwischen den Bildern ist und F(t) der Emissionswert zu einem bestimmten Zeitpunkt des Abklingens ist.Assuming an exponential decay behavior, the decay time (τ) can be determined by the following equation: $$\mathrm{\tau }=\mathit{\Delta t}/\mathit{ln}\frac{E\left(t_1\right)}{E\left(t_2\right)}\mathrm{with}E\left(t_1\right)=E_0{e}^{-\frac{t_1}{\tau }}\mathrm{and}E\left(t_2\right)=E_0{e}^{-\frac{t_2}{\tau }};$$

where Δt is the time interval between the images and F(t) is the emissivity at a particular time of the decay.

These values can be determined from a histogram of the images or the image difference.

The spectral distribution of the emission of the phosphor can be determined from the color coordinates for different images, where: $$K_R=\frac{R}{R+G+B}\mathrm{and}{K}_G=\frac{G}{R+G+B}.$$

Furthermore, a comparison of an additional start image recorded before the activation of the excitation radiation with the images of the image series recorded during the decay time and with the last image (reference image) is possible.

The presence of the security feature in the area of the receiving frame can be verified by the comparison and the authenticity of the security document can subsequently be checked. In particular, the authenticity and integrity of the security document can be checked by verifying the security feature on the security document.

The reference image, which is the last image in the series of images, is generated in a predetermined time frame, in particular in the ms range, as a result of which emissions with decay times greater than the ms range are also filtered out. For this purpose, the reference image can be compared with the start image recorded before activation of the excitation radiation.

• Referenzprüfung, Vergleich des letzten Bilds (Referenzbild) aus der Serienaufnahme mit einem vor der Anregung aufgenommenen Startbild;
• Detektion des Sicherheitsmerkmals und
• Bestimmung der Emissionseigenschaften (τ, λ) des Sicherheitsmerkmals bzw. dessen Leuchtstoff.

In one embodiment of the method, the authenticity of the security feature is checked using the following features:

• Reference check, comparison of the last image (reference image) from the series recording with a start image recorded before the excitation;
• detection of the security feature and
• Determination of the emission properties ( τ , λ ) of the security feature or its phosphor.

The recording speed when generating the series of images is selected in such a way that fluorescent phosphors or features with short decay times, i.e. in the ps range, are ruled out as non-verifiable, since such short emissions are not recorded with sufficient intensity. By means of a reference test, in which the last image in the recording is compared with the start image recorded before excitation, phosphors with long decay times are ruled out as non-verifiable. If one of the two above features indicates a fluorescent or phosphorescent phosphor, then the result of the authenticity of the security feature is output as "false".

In addition to the presence of the phosphor sought in the security feature, the external shape of the security feature can also be checked. Correspond to the detected phosphor and the security feature does not match the stored data of the predetermined phosphor or security feature, the authenticity is determined as "false". For the emission properties feature, the spectral distribution of the radiation emitted by the phosphor and the decay time of the phosphor of the security feature are checked. If the spectral position and the decay time of the phosphor match the stored values, and if the other features are still positive ("genuine"), the verification shows that the security feature is "genuine".

The optional object recognition preferably includes various image processing steps, such as filter applications for noise reduction, contrast adjustment or color channel enhancement, a shape analysis for detecting the security feature. The noise can be reduced, for example, by means of morphological filters such as erosion or dilatation. Template matching can be used for shape analysis. The Fast Fourier Transform (FFT) of the images can also be used.

In a further method step, which makes sense above all in strong ambient light, the distance between the security document with the security feature and the image capture unit of the smartphone is selected to be smaller than the distance of the focusing range of the image capture unit. No optical focusing or focus adjustment is required. The distance between the smartphone camera and the security feature when capturing the images can therefore be chosen to be very small, since no sharp images are required for the present method because only the emission and, if necessary, the shape of the security feature are captured. The small distance between the security feature and the camera has the advantage that more energy is available for exciting the phosphor of the security feature, and that the emission of the phosphor is recorded over a wide solid angle. The minimization of the distance between the camera and the security feature is particularly important due to the quadratic dependency of the intensity of the flash light on the distance to the excitation source or the emission on the distance to the detection unit. In this way, a comparatively low emission can also be recorded, which would no longer be detectable when taking a picture in the focussing range. This reduces the false rejection rate (ie a genuine security document is evaluated as false). For example, standard smartphones have a focus range of 60 mm. A distance of between 10 mm and 80 mm between the image capturing unit and the security document with security feature is therefore preferably used for recording the images for the method. The distance between the image capture unit and the security document with the security feature during the image recording is particularly preferably less than 50 mm. Another advantage of using blurred images is to reduce the resolution of the images, thereby speeding up the processing of the images.

In another embodiment of the method for verifying the security feature, a reference area is selected next to the area of the security feature, ie next to the area of the phosphor. Preferably, the two areas have the same visible body color. This can be used to compensate for exposure fluctuations during recording under artificial light (50 Hz flickering). The positions of the phosphor and the reference area are preferably on predefined in the security document (e.g. relative to a prominent character on the document). For the verification, an equal number of pixels in both areas is selected for all captured images and an image difference for these sections is created for each image.

An additional verification factor can be used for certain phosphors, in particular silicate garnets. These phosphors show a broad emission spectrum with local maxima in the green and red spectral range, which also have different decay times. As a result, a characteristic color shift is detected in decay measurements over the entire visible spectral range, which can also be used as an authenticity criterion.

A further advantage of the method is that the known smartphone, which is available to a large number of users, can be used as a mobile terminal device for verifying the security feature. A quick, internal evaluation and authentication of the fluorescent emissions measured with the smartphone is carried out. It is also advantageous that the distance between the security feature and the image capturing unit can be kept small, since at the same time the security feature is covered from ambient light, such as daylight or room light.

The method with its method steps is preferably provided as an application or app for the smartphone.

The image frequency of the image sensor used (in particular a smartphone camera) determines a lower limit, which must be reached through the decay behavior of the phosphor.

An upper limit is given by the physiological properties of human vision, in particular by visual perception, ie the reception and processing of optical stimuli by the eye and the brain. In order to be able to assign the phosphor used in the security feature to a high security level, the emission of the security feature should not be detectable by human visual perception. In particular, the decay time of the phosphor should be less than 1 s, since after 1 s the phosphor begins to glow, which can be perceived by humans. The phosphor is chosen so that its decay time is in the single-digit or double-digit ms range. The decay time of the phosphor (always considered from the time the excitation source is switched off) of the security feature is preferably in the range from 1 ms to 50 ms. The phosphor of the security feature particularly preferably has a decay time of 10 ms to 30 ms.

So that the security feature can be detected solely by means of a mobile device (especially a smartphone), the phosphor is configured in such a way that it can be excited in the visible spectral range, in particular in the blue spectral range, so that the flash light source of the smartphone can deliver this excitation radiation. Furthermore, the phosphor is configured in such a way that it emits in the visible spectral range, with this emission not being detectable by the user through visual perception due to the short decay time.

The white light of the lighting unit of a smartphone is generated by an LED, which consists of an LED semiconductor chip with an emission at around 450 nm and LED conversion phosphors placed above the LED semiconductor chip, the conversion phosphors reflecting the emission of the convert blue LED proportionately into longer-wavelength visible luminescence radiation (broadband emission in the green, yellow and red spectral range) with an emission maximum of around 560 nm, for example. The white light of the LED available as the lighting unit of commercially available smartphones results from the additive color mixture of the individual luminescence components described, with the blue spectral component having the higher intensity. This means that the phosphor that can be used to provide the security feature according to the invention must preferably be configured in such a way that it has a high efficiency of spectral excitability, particularly in the range between 420 nm and 470 nm. The phosphor particularly preferably has an effective excitation wavelength of 450 nm.

The smartphone camera is available as an image acquisition unit for detecting the luminescence signals of the phosphor. The image acquisition unit is preferably a CMOS sensor which is equipped with an IR filter, as a result of which there is a spectral sensitivity of up to approximately 750 nm. Single images, series of images or videos can be recorded by means of the image acquisition unit.

In principle, the method according to the invention can be used in various test devices. Such testing devices can be used as a retrofit module for stationary testing (e.g. in ATMs) or preferably designed as a mobile terminal device. The mobile end device is preferably a smartphone, but can also be a tablet or another similar multifunctional data processing device that includes a camera with an image capture unit and/or a lighting unit and a data processing unit. The data processing unit is preferably a Processor, in particular a microprocessor. The test can also be carried out using stationary terminals or other data processing systems with image acquisition units (e.g. desktop monitors or service terminals).

The phosphor is preferably arranged in the security feature in such a way that it forms a pattern. The phosphor, in particular the luminescence pigments of the phosphor, are preferably applied to a carrier as a defined pattern. The pattern can be arranged as a shape such as a triangle or a star. Alternatively, the pattern of the security feature formed by the phosphor can contain data and be arranged as a code, for example a QR code.

The pigments of the phosphor are printed as a security feature, for example, on a security document or on a layer of a security document. The printing or application of the phosphor on the security document can be carried out using known printing methods such as e.g. B. gravure printing, flexographic printing, offset printing, screen printing or digital printing processes. Furthermore, the phosphor can be applied to the security document by coating processes or lamination processes.

An authenticity check and/or integrity check can be carried out. The security feature can only be verified by selecting the phosphor with a decay time in the ms range. It has proven to be advantageous that, due to the specially selected phosphor, its emissions can still be reliably measured even after the end of the excitation process. Both the phosphor can be verified via the decay time and the emission spectrum, as well as by the Fluorescent formed patterns as a further safety factor. A high degree of security against counterfeiting can thus be achieved by combining several factors. For secure authentication of a security document with the security feature, this can be arranged, for example, in an area of a further security feature, such as an image.

The security feature can be applied to different security documents, for example a bank note, an identity card, a passport, a driver's license, a ticket, a stamp or the like.

Fig. 1

eine Ausführungsform eines erfindungsgemäßen Sicherheitsmerkmals auf einem Geldschein;

Fig. 2

eine schematische Darstellung von Komponenten einer erfindungsgemäßen Anordnung zur Verifikation des Sicherheitsmerkmals;

Fig. 3

ein Diagramm mit dem An- und Abklingverhalten eines Leuchtstoffes des Sicherheitsmerkmals bei Blitzlichtanregung;

Fig. 4

ein Ablaufplan zur Durchführung der Verifikation des Sicherheitsmerkmals mit der erfindungsgemäßen Anordnung.

Further details, advantages and developments of the invention result from the following description of preferred embodiments of the invention, with reference to the drawing. Show it:

1

an embodiment of a security feature according to the invention on a bank note;

2

a schematic representation of components of an inventive arrangement for verification of the security feature;

3

a diagram with the rise and fall behavior of a phosphor of the security feature when excited by a flash light;

4

a flow chart for carrying out the verification of the security feature with the arrangement according to the invention.

1 shows a security feature 01 according to the invention, which is applied to a document of value, namely a security document 02 in the form of a bank note, which is represented symbolically. The security feature can be used to verify security document 02. The security feature 01 has the shape of a star here. It is positioned below a visible feature 03, here the face value of the banknote. The security feature 01 consists of a phosphor that can be excited to luminesce by means of electromagnetic radiation with a predetermined wavelength, as mentioned above and explained in detail in the applicant's further patent application that is included.

The security feature 01 can be verified using a method in which the authenticity of the security feature 01 is checked.

2 shows a schematic arrangement for verifying the security feature 01, the security feature 01 being excited to luminescence by means of an illumination unit 04 of an image recording unit 06 of a mobile terminal device, in particular a smartphone 07, in that the illumination unit 04 generates excitation light, in particular a flashlight 08. The flashing light 08 of the image recording unit 06 is generated by means of an LED emitting white light. The flashlight 08 has an intensity I _A . After excitation, the phosphor of security feature 01 emits electromagnetic radiation, which occurs for a decay time in the ms range after excitation has ended. The emission I _E of the phosphor can be detected with a camera or a detector 09 of the image recording unit 06. Furthermore, the detector 09 detects an impinging on the security feature 01 and the bank note 02 and reflected on them Ambient radiation I ₀ of daylight or room light. The ambient radiation I ₀ is kept low in the method according to the invention, since a distance d between the security feature 01 and the smartphone 07 can be kept small. Due to the small distance d, which is below the focusing range (focus) of the image recording unit 06, the smartphone 07 shields the ambient radiation I ₀ for the most part.

In 3 a diagram with the rise and fall behavior of the phosphor used in security feature 01 is shown. An emission curve 11 of the security feature 01 excited to luminescence is shown in the diagram along a time axis t. Furthermore, a flash light excitation curve 12 is plotted along the time axis. If the flash is fired using the smartphone 07 ( 2 ) is generated, the flashlight excitation curve 12 rises steeply, holds its level for a short time and then falls to zero after the flashlight has gone out. The phosphor of the security feature 01 is excited to luminescence by the electromagnetic radiation of the flash light, as a result of which its emission curve 11 rises almost simultaneously with the flash light emission curve 12, regularly with a reduced steepness. After the flash light has gone out, the emission curve 11 drops significantly more slowly than the flash light excitation curve. According to the invention, the decay behavior of the phosphor is in the ms range.

Below the timeline are in 3 individual through the detector 09 of the smartphone 07 ( 2 ) Captured images 13 of the security feature 01 are shown. The images 13 show the decaying emission of the security feature 01 as a pattern that becomes weaker over time. For the verification of the security document 02 you can use another Process step are used. After the emission has essentially decayed completely, a reference image 14b can be recorded as the last image of the recorded image sequence. Depending on the evaluation method, an additional reference image 14a can also be recorded before the activation of the excitation radiation (triggering of the flash). An additional check of the security feature is possible, for example, by comparing the reference images 14a and 14b with one another.

4 shows in a simplified form the basic process of verifying the security feature 01 using the in 3 arrangement shown. In a positioning step 41, the secure document to be verified is positioned in such a way that it can be securely captured by the smartphone's image capture unit. In an optional reference check step 42, the start image 14a of the security feature is already generated before the triggering of the flash light excitation of the smartphone. In a detection step 43, a single flash is triggered with the help of the image recording unit of the lighting unit of the smartphone and a serial image or video recording is carried out in order to record the luminescence signals of the phosphor used to create the security feature that are present after the end of the flash light excitation and decay in the ms range. Finally, in an emission analysis step 44, the recorded series of images and the reference recordings are compared using the data processing unit. In addition to the calculation of the image differences and their analysis, other image processing methods such as contrast adjustment and histogram analysis of the different color channels are used in order in this way to determine both the spectral emission and the exclusive decay characteristics of the to verify the phosphor used. In an optional extraction step, object recognition can be performed. The authenticity of the checked security document can be confirmed in a release step 45 by comparing the calculated parameters with the authenticity parameters of the security feature that are preferably stored in the data memory of the smartphone. In particular, the authenticity and integrity of the security document can be confirmed by the verification of the security feature on the security document.

Reference List

01

security feature

02

Security document / bill / banknote

03

face value

04

lighting unit

05

-

06

image acquisition unit

07

smartphone

08

flashlight

09

detector / camera

10

-

11

emission curve

12

flash excitation curve

13

Image recording of the security feature 01

14a

splash screen

14b

reference image

41 - 45

process steps

Claims (8)

1. A method for verifying, by means of a smartphone, a phosphor-based security feature containing a phosphor that can be excited to emission and that has a decay time in the ms range, comprising the steps:

   - exciting the phosphor of the security feature to emission by means of an illumination unit of the smartphone;

   - capturing the emission upon completion of the excitation during a predetermined decay time through capture of a series of images or of a video recording with an image capture unit of the smartphone;

   - evaluating the series of images or video recording by means of a data processing unit of the smartphone, wherein the emission captured during the decay time is compared with stored reference data in order to verify the authenticity of the security feature;

   characterized in that the distance between the security feature and the image capture unit of the smartphone during the excitation of the phosphor and the capture of the emission is selected to be less than the range of focus of the image capture unit.
2. The method according to claim 1, characterized in that, for the evaluation of the series of images, the emission properties decay time (τ), wavelength (A) and/or colour shift are determined and compared with the reference data.
3. The method according to claim 1 or 2, characterized in that, for the capture of the emission, the image differences between the images captured during the decay time and the reference image captured after the emission has decayed are generated (Δ_1R=B₁ -B_ref ... Δ_nR=B_n -B_ref) and in that the emission values are subsequently calculated in the form of a hue value of the different colour channels by means of an RGB histogram and the decay time of the phosphor is determined on this basis.
4. The method according to claims 1 to 3, characterized in that the following steps are carried out prior to the excitation of the phosphor:

   - implementation of an object detection by means of the image capture unit and the data processing unit of the smartphone to determine the position of the security feature on the security document or positioning the smartphone over the security document according to a predetermined position frame displayed in a display of the smartphone and using a position feature of the security document over which the position frame is arranged;

   - definition of a capture frame using the determined position of the security feature, wherein the security feature is arranged in the area of the capture frame;

   - defining a reference area arranged indirectly adjacent to the capture frame;

   and in that, upon completion of the excitation, the series of images is captured in the area of the capture frame as well as in the reference area.
5. The method according to claim 4, characterized in that the series of images captured in the capture frame is compared with the series of images captured in the reference area by means of the data processing unit.
6. The method according to one of claims 1 to 5, characterized in that the capture time is selected so that the last image of the series of images is captured after the decay time has ended, and in that the security feature is only verified as genuine when no emission of the phosphor is detectable in this last image.
7. The method according to claim 6, characterized in that one or more images from the series of images of the position frame is compared with the last image of the series of images by means of the data processing unit of the smartphone in the following sub-steps:

   - emission detection, wherein an image difference between the captured images and the reference image is respectively determined, an RGB histogram is generated, the hue value of the different colour channels is determined, and the decay time of the phosphor is determined; and

   - object determination, wherein a shape analysis of the security feature is carried out.
8. The method according to one of claims 1 to 7, characterized in that an application (app) is installed on the mobile end device, which application controls the illumination unit, the image capture unit and the data processing unit in order to execute the method.

Images