METHOD FOR VERIFYING THE AUTHENTICITY OF A FLUENTIAL-BASED SECURITY FEATURE USING A MOBILE DEVICE AND MOBILE DEVICE

Description

[0001] The present invention relates to a method for authenticating a phosphor-based security feature using a mobile device. The invention also relates to a mobile device with an application (app) for implementing the method.

[0002] Security features are used to protect valuable or security documents against counterfeiting. These can be, for example, an identity document, a check card, a non-personalized authorization card such as a ticket or a means of payment, or a valuable or security element intended for product security.

[0003] It has long been known in the art to provide valuable or security documents with security features in the form of luminescent substances to make them more forgery-proof. Arrangements and methods for reliably verifying such luminescent security features using a mobile device are described in the applicant's publications DE 10 2018 109 141 A1, DE 10 2018 109 142 A1, and DE 10 2018 102 015 A1.

[0004] In the procedures described therein, due to the use of the mobile device, the authenticity checks are subject to a wide variety of environmental conditions, in particular the different lighting conditions, which can make the detection of phosphor-based security features more difficult.

[0005] US Patent No. 10,572,638 B2 describes a mobile terminal for capturing a person's biometric data. The camera's beam path is folded several times to ensure that no "bulbous nose" is captured.

[0006] US Pat. No. 7,079,230 B1 also describes a method and system for authenticating a packaged object. A photoluminescent material is applied to the object, allowing verification of the authenticity of the product or its packaging. The smartphone's light source is moved over the surface of the photoluminescent label, thus stimulating it. The label's response is captured by a detector and further processed. The intensity of the irradiation can be adjusted depending on the ambient light.

[0007] The object of the present invention is to provide a method for authenticity verification of a phosphor-based security feature using a mobile terminal that delivers a reliable test result even under varying ambient light conditions. Furthermore, the object of the invention is to provide a mobile terminal for carrying out the method.

[0008] This object is achieved by a method having the features of claim 1 and by a mobile terminal having the features of claim 13. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0009] The method according to the invention for authenticity verification of a phosphor-based security feature using a mobile terminal comprises in particular the following steps: Detecting a radiant intensity of the ambient light, specifying at least one parameter for an excitation of the phosphor-based security feature depending on the detected radiant intensity of the ambient light, positioning the security feature with respect to the image recording device while setting or maintaining the at least one parameter for the excitation, exciting the phosphor of the phosphor-based security feature for emission by means of the illumination device, detecting the emission of the light emitted by the phosphor-based security feature by means of the camera, evaluating a series of images or video recording captured by the camera by means of the evaluation device and assessing the authenticity of the phosphor-based security feature based on reference data.

[0010] This has the advantage that a simple mobile device, in particular a commercially available smartphone, can be used to verify the authenticity of a phosphor-based security feature, which is also designed to take into account the lighting conditions prevailing during the verification.

[0011] Detecting the ambient light intensity using the camera itself contributes to reducing component complexity. However, it is also possible to use a brightness sensor associated with the mobile device, which is also configured to detect the ambient light intensity, as an alternative or in addition.

[0012] It is advantageous if the at least one parameter for the excitation of the phosphor-based security feature is the distance between the image recording device and the phosphor-based security feature, and if excitation of the phosphor-based security feature is only possible when the predetermined distance is present as a function of the radiant intensity of the ambient light. Thus, an authenticity check can only be carried out when the mobile terminal is at a predefined distance from the phosphor-based security feature or the valuable document on which it is applied. This distance varies depending on the detected ambient light, with real-time detection of the ambient light intensity and real-time adjustment of the predetermined distance for the excitation of the security feature preferably taking place.In this way, shadowing caused by the mobile device can be taken into account during real-time verification.

[0013] Additionally, there is also the advantageous possibility that the at least one parameter for the excitation of the phosphor-based security feature is the luminosity of the lighting unit, and that excitation of the phosphor-based security feature is only possible when the luminosity specified for excitation of the phosphor-based security feature, depending on the radiant intensity of the ambient light, is present. Thus, reliable excitation of the phosphor-based security feature can occur even at greater distances, because the intensity emitted by the lighting unit is adjusted depending on the available ambient light.

[0014] Additionally, the at least one parameter for stimulating the phosphor-based security feature can be the exposure time. "Exposure time" essentially refers to the duration of illumination during which the illumination unit emits light toward the security feature.

[0015] According to the invention, real-time (image) capture is performed by the camera even before the phosphor-based security feature is excited, with the image captured by the camera being simultaneously displayed on the mobile device's display. The image displayed on the display is overlaid with a partially transparent mask that has a positioning frame or contour adapted to the feature to be captured. The dimensions of the positioning frame or contour are specified depending on the detected radiant intensity of the ambient light. In this way, authenticity verification can be performed under conditions that are specified and adjusted depending on the incident ambient light.

[0016] According to the invention, excitation of the phosphor-based security feature is only possible once the positioning frame or contour in the image has been aligned with the dimensions of the phosphor-based security feature. This allows for an optimized distance between the camera and the security feature, allowing for improved authentication.

[0017] The user-friendliness of the mobile device for the authenticity verification of the phosphor-based security feature is further increased by the fact that the excitation of the phosphor-based security feature is carried out automatically when the positioning frame or the positioning contour in the image has been aligned with the dimensions of the phosphor-based security feature.

[0018] For even more reliable detection and verification of the authenticity of the phosphor-based security feature, it is also advantageous if a white balance is carried out during or after the detection of the phosphor-based security feature depending on the radiant intensity of the ambient light.

[0019] It is possible for the mobile device to additionally detect at least one environmental parameter and evaluate it by the evaluation device. Examples of environmental parameters include the geographical position detected by a GPS sensor, movement information detected by inclination sensors and / or acceleration sensors, and data on mechanical vibrations of the mobile device. Thus, the environmental parameters can be used to analyze the environment of the mobile device and draw conclusions about the presence of an anomaly with respect to at least one environmental parameter (anomaly detection). For example, a phosphor-based security feature can also be classified as "counterfeit" based on the detection of an environmental anomaly.

[0020] The image series or video recording is preferably always captured for a specified minimum duration during the decay time of the emission of the phosphor-based security feature. After the excitation has ended, the decay behavior of the phosphor-based security feature can be examined and evaluated, with the recorded decay curve or emission curve being compared with a reference curve. If a discrepancy is found between the reference curve and the emission curve, it can also be concluded that a counterfeit phosphor-containing security feature or a valuable or security document containing one is counterfeit. The same applies to the decay time.

[0021] The corresponding reference values ​​are stored, for example, in a digital memory that may be part of the mobile device or in an intelligent database on a remote server.

[0022] Preferably, emission detection and shape analysis are performed when assessing the authenticity of the phosphor-based security feature. During emission detection, several images from a series of images recorded by the camera are compared. In particular, an image difference between the captured images and the reference image is determined, an RGB histogram is created, the hue value of different color channels is determined, and the decay time of the phosphor is determined. During shape analysis, the shape of the security feature is compared with a reference shape.

[0023] To ensure the security feature can be detected using a smartphone alone, the phosphor is configured to be excitable in the visible spectral range, particularly in the blue spectral range, so that the smartphone's flash light source can deliver this excitation radiation. Furthermore, the phosphor is configured to emit in the visible spectral range to ensure that it can be detected with the camera module of a standard smartphone. Furthermore, the phosphor is configured so that its luminescence decays in the millisecond range after the flash light excitation has ended, enabling secure verification after the excitation has ended.

[0024] In a preferred embodiment, the phosphor of the phosphor-based security feature is a Ce 3+< or Mn 2+< co-doped silicate garnet phosphor. The stationary luminescence of the phosphor, upon excitation with the light of a white-emitting LED, preferably at a maximum wavelength of 450 nm, exhibits a broadband emission spectrum with multiple emission maxima in the visible spectral range. These maxima are located at approximately 505 nm (attributable to the emission of Ce 3+< ions on dodecahedral Ca 2+< sites), 570 nm (attributable to the sensitized emission of Mn 2+< ions on dodecahedral Ca 2+< sites), and 700 nm (attributable to the sensitized emission of Mn 2+< ions on octahedral Sc 3+< sites).

[0025] The white light of a smartphone's lighting unit is generated by an LED, which consists of an LED semiconductor chip emitting at approximately 450 nm, for example, and one or more LED conversion phosphors positioned above the LED semiconductor chip. These conversion phosphors are capable of partially converting the emission of the blue LED into longer-wavelength visible luminescence radiation (broadband emissions in the green, yellow, and red spectral ranges) with an emission maximum of approximately 560 nm, for example. The white light of the LED used as the lighting unit in commercially available smartphones results from the additive color mixing of the individual luminescence components described above, with the blue spectral component exhibiting the significantly higher intensity.This means that the phosphor used to provide the security feature according to the invention must preferably be configured such that it exhibits a high efficiency of spectral excitability, particularly in the range between 420 nm and 470 nm. The maximum spectral excitability of the phosphor is particularly preferably at approximately 450 nm.

[0026] The smartphone camera serves as the image capture unit for detecting the luminescence signals of the phosphor. The image capture unit is preferably equipped with a CMOS sensor and an IR filter. It thus has a spectral sensitivity that covers the entire visible spectral range up to approximately 750 nm. The image capture unit can be used to record individual images, image series, or video recordings. This means that the phosphor used to create the security feature must be configured so that, after excitation, it emits with the highest possible intensity, preferably in the spectral range between 480 nm and 750 nm.

[0027] The mobile terminal used according to the invention for verifying the authenticity of the security feature is preferably a conventional, commercially available

[0028] A smartphone equipped with a suitable application program (app). It will be understood by those skilled in the art that the same functionality can also be integrated into a tablet or a similar multifunctional data processing device, for which purpose it must be equipped with a camera with an image capture unit and / or lighting unit as well as a data processing unit. Such devices with equivalent functions are also intended to be encompassed by the invention. Preferably, the evaluation device is a processor, in particular a microprocessor. The processor comprises a digital memory into which a computer program (an app) with software code sections is or can be directly loaded, which initiates and executes the steps of the aforementioned method when the program is executed by the processor.

[0029] The present invention is explained in more detail below with reference to figures, whereby the illustrated examples are merely exemplary and do not represent a limitation with regard to the scope of the described invention. They show in detail: Fig. 1 is a schematic representation of a value or security document in the form of a banknote with a phosphor-based security feature, Fig. 2 is a schematic representation of components of an arrangement for authenticity verification of the phosphor-based security feature, Fig. 3 is a diagram showing the rise and fall behavior of a phosphor of the security feature when excited by a flash light, Fig. 4 is a schematic plan view of the display of a mobile terminal in which the distance between the terminal and the security feature is too great, and Fig. 5 is a schematic plan view of the display of a mobile terminal in which the distance between the terminal and the security feature is optimal for its authenticity verification.

[0030] Figure 1shows a value or security document 100 in the form of a banknote, which includes a phosphor-based security feature 102. The security feature 102 can be used to verify the security document 100. The phosphor-based security feature 102 has a star shape here. The star shape is chosen purely for illustrative purposes; therefore, it can also have any other shapes. The phosphor-based security feature 102 is arranged in the region of a visible feature 104, here in the form of the nominal value of the banknote. The security feature 102 consists of a phosphor that can be excited to luminescence by means of electromagnetic radiation with a predetermined wavelength, as mentioned above. The security feature 102 can be verified using a method, wherein the authenticity of the security feature 102 is checked, which will be discussed in more detail below.

[0031] Figure 2shows a schematic arrangement for verifying the phosphor-based security feature 102, wherein the security feature 102 is excited to luminescence by means of an illumination unit 204 of an image recording device 202 of a mobile terminal 200, in particular a smartphone, in that the illumination unit 204 generates excitation light, in particular a flash light. The flash light of the illumination unit 204 of the image recording device 202 is generated by means of a white light-emitting LED. The flash light has an intensity IA . After excitation, the phosphor of the security feature 102 emits electromagnetic radiation, which persists for a decay time in the ms range after the end of the excitation. The emission IE of the phosphor can be detected by a camera 204 or a detector of the image recording device 202.Furthermore, the camera 204 is configured to detect ambient radiation I 0 of daylight or room light that strikes and is reflected by the security feature 102 and the banknote. The smartphone can also be equipped with a brightness sensor (photosensor) to detect the intensity of the ambient light. The ambient radiation I 0 is to be kept as low as possible during the detection process of the phosphor-based security feature 102, with a distance d between the security feature 102 and the smartphone being kept small. Due to the small distance d, which is preferably below the focusing range (focus) of the camera 206, the smartphone largely shields the ambient radiation I 0, although this is not absolutely necessary for the method according to the invention.

[0032] In Figure 3A diagram showing the rise and fall behavior of the phosphor used in the security feature 102 is shown in the diagram. An emission curve 300 of the security feature 102 excited to luminescence is shown along a time axis t. Furthermore, a flash excitation curve 302 is plotted along the time axis. If the flash is generated by the smartphone, the flash excitation curve 302 rises steeply, maintains its level for a short time, and drops to zero after the flash has gone out. The electromagnetic radiation of the flash excites the phosphor of the security feature 102 to luminescence, as a result of which its emission curve 300 rises almost simultaneously with the flash emission curve 302, usually with a reduced steepness. After the flash has gone out, the emission curve 300 falls significantly more slowly than the flash excitation curve 302. The decay behavior of the phosphor is in the ms range.Also shown below the time axis are individual images 304 of the security feature 102 captured by the camera 206 of the mobile terminal 200. The images 304 show the fading emission of the security feature 102 as a pattern that weakens over time. They can be used for the verification of the security document 100 in a further process step. After the emission has essentially completely faded away, a reference image 306 can be captured as the last image of the captured image sequence. Depending on the evaluation method, an additional reference image 308 can also be captured before the activation of the excitation radiation (triggering the flash). An additional check of the security feature is possible, for example, by comparing the reference images 306 and 308 with each other.

[0033] To verify the authenticity of the phosphor-based security feature 102 using the mobile terminal 200, the following steps are performed: Detecting the radiant intensity I 0 of the ambient light, specifying at least one parameter for exciting the phosphor-based security feature 102 as a function of the detected radiant intensity I 0 of the ambient light, positioning the security feature 102 with respect to the image recording device 202 while setting or maintaining the at least one parameter for the excitation, exciting the phosphor of the phosphor-based security feature 102 for emission by means of the illumination unit 204, detecting the emission of the light emitted by the phosphor-based security feature 102 by means of the camera 206, evaluating a series of images 304 or video recording captured by the camera 206 by means of the evaluation device 208, and assessing the authenticity of the phosphor-based security feature 102 based on reference data 306, 308.

[0034] The at least one parameter for the excitation of the phosphor-based security feature 102 is, in this case, the distance d between the image recording device 202 and the phosphor-based security feature 102. Excitation of the phosphor-based security feature 102 is only possible when the predetermined distance d is present as a function of the radiant intensity I 0 of the ambient light. Alternatively, it is also possible for the excitation luminous intensity IA to be increased based on the detected ambient light so that a desired luminescence effect occurs.

[0035] According to Figures 4 and 5Real-time capture is performed by camera 206 even before the phosphor-based security feature 102 is excited, with the image captured by camera 206 being output in real time on display 210 of mobile terminal 200. The image output on display 210 is overlaid by a partially transparent mask 310, which has a positioning frame adapted to the feature 102 to be captured or a positioning contour 312 adapted to the feature to be captured. The dimensions of the positioning frame or the positioning contour 312 are predetermined or adjusted depending on the detected radiant intensity I 0 of the ambient light. The mask 310 or positioning contour 312 is therefore variable with regard to its display size on display 210.

[0036] According to the invention, excitation of the phosphor-based security feature 102 is only possible when the positioning frame or the positioning contour 312 in the image has been aligned with the dimensions of the phosphor-based security feature 102.

[0037] In Figure 4 The ambient light intensity I 0 was determined, with a high value for I 0 being present. This means that the mask 310 was chosen to be correspondingly small, which means that the smartphone must be brought very close to the value or security document 100 in order to align the contours of the security feature 102 and the positioning contour 312.

[0038] The closer the smartphone is brought to the security feature 102, the stronger its shadowing becomes compared to the ambient light, so that the size of the mask 310 can be readjusted. The excitation of the phosphor-based security feature 102 is then carried out automatically when the positioning frame or the positioning contour 312 in the image has been aligned with the dimensions of the phosphor-based security feature 102, as shown in the illustration according to Figure 5 is illustrated for the case of congruence.

[0039] As a result, the ambient light can be reliably taken into account in the authenticity verification of the phosphor-based security feature 102 using the method according to the invention and the mobile terminal 200 according to the invention, thus creating an improved and more reliable testing option. LIST OF REFERENCE SYMBOLS

[0040] 100Value or security document 102Luminous-based security feature 104Visible feature 200Mobile device / smartphone 202Image capture device 204Illumination unit (image capture device) 206Camera (image capture device) 208Evaluation device / microprocessor 210Display 300Emission curve 302Flash excitation curve 304Image 306Reference image 308Additional reference image 310Mask (partially transparent) 312Positioning contour

Claims

1. A method for verifying the authenticity of a fluorescent-based security feature (102) using a mobile device (200) which has at least one evaluation device (208), an image recording device (202) with a camera (206) and an illumination unit (204), and a display (210), comprising the steps of: - detecting of an ambient light intensity (I0) of the ambient light, - presenting of at least one parameter for excitation of the fluorescent-based safety feature (102) as a function of the detected radiant intensity (I0) of the ambient light, - positioning the security feature (102) with respect to the image recording device (202) while setting or maintaining the at least one parameter for the excitation, - stimulating the fluorescent material of the fluorescent-based security feature (102) for emission by means of the illumination unit (204), - detecting the emission of the light emitted by the fluorescent-based security feature (102) by means of the camera (206), - evaluating of an image series (304) or video recording captured by the camera (206) by means of the evaluation device (208) and evaluation of the authenticity of the fluorescent-based security feature (102) on the basis of reference data (306, 308), characterized in that real-time detection by means of the camera (206) takes place even before the excitation of the fluorescent-based security feature (102) and the image detected by the camera (206) is output on the display (210), the image output on the display (210) being superimposed with a partially transparent mask (310) which has a positioning frame adapted to the feature (102) to be detected or a positioning contour (312) adapted to the feature to be detected, and in that the dimensions of the positioning frame or the positioning contour (312) are predetermined as a function of the detected ambient light intensity (I0 ), with excitation of the fluorescent-based security feature (102) only being possible when the positioning frame or the positioning contour (312) in the image has been brought into coincidence with the dimensions of the fluorescent-based security feature (102).

2. The method according to claim 1, characterized in that the ambient light intensity (I0) is detected by means of the camera (206).

3. The method according to claim 1 or 2, characterized in that the ambient light intensity (I0) is detected by means of a brightness sensor of the mobile device (200).

4. The method according to one of claims 1 to 3, characterized in that the at least one parameter for the excitation of the fluorescent-based security feature (102) is the distance (d) between the image recording device (202) and the fluorescent-based security feature (102), and in that excitation of the fluorescent-based security feature (102) is only made possible when the predetermined distance (d) is present as a function of the light intensity (I0 ) of the ambient light.

5. The method according to one of claims 1 to 4, characterized in that the at least one parameter for the excitation of the fluorescent-based security feature (102) is the luminous intensity (IA ) of the illumination unit (204), and in that excitation of the fluorescent-based security feature (102) is only possible when the luminous intensity (IA ) for excitation of the fluorescent-based security feature (104), which is predetermined as a function of the light intensity (I0 ) of the ambient light, is present.

6. The method according to any one of claims 1 to 5, characterized in that the at least one parameter for the excitation of the fluorescent-based security feature (102) is the exposure time.

7. The method according to any one of claims 1 to 6, characterized in that the excitation of the fluorescent-based security feature (102) is performed automatically when the positioning frame or the positioning contour (312) in the image has been brought into coincidence with the dimensions of the fluorescent-based security feature (102).

8. The method according to any one of claims 1 to 7, characterized in that during or after the detection of the fluorescent-based security feature (102), a white balance is performed as a function of the light intensity (I0) of the ambient light.

9. The method according to any one of claims 1 to 8, characterized in that at least one environmental parameter is additionally recorded by the mobile device (200) and evaluated by the evaluation device (208).

10. The method according to any one of claims 1 to 9, characterized in that the acquisition of the series of images (304) or the video recording is performed for a predetermined minimum duration during a decay time of the emission of the fluorescent-based security feature (102).

11. The method according to any one of claims 1 to 10, characterized in that an emission detection and a shape analysis are performed during the evaluation of the authenticity of the fluorescent-based security feature (102).

12. A mobile device (200) having a processor (208) forming an evaluation device, having an image recording device (202) which comprises a camera (206) and an illumination unit (204), having a display (210), and having a digital memory of the processor into which a computer program with software code sections is or can be loaded directly, which causes the steps of the method according to at least any one of claims 1 to 11 to be carried out.