DE102019106437A1 - Device for detecting a surface defect of an identification document - Google Patents

Abstract

The invention relates to a device 100 for detecting a surface defect of an identification document. The device 100 comprises a light source 101 which is designed to emit directed light in the direction of a surface of the identification document, the directed light being reflected on the surface of the identification document. The device 100 further comprises a camera 103 which is designed to detect the reflected light from the surface of the identification document in order to obtain an image of the identification document, the image of the identification document having an inhomogeneity which indicates the surface defect. The device 100 further comprises a detection device 105 which is designed to determine a position of the inhomogeneity in the image of the identification document in order to detect the surface defect of the identification document. The device 100 can furthermore comprise a print inspection device 107 which is designed to carry out a print inspection of the identification document on the basis of an unmasked image and a pre-stored reference image.

Description

The present invention relates to the field of quality assurance in the production of identification documents, in particular the detection of surface defects.

With the automatic optical inspection of real, patterned and inhomogeneous surfaces for possible surface defects, in particular disturbances that disturb the evenness of the surface in a local environment, such as scratches, soiling, unwanted fibers, or film and paint residues, the problem of unambiguous arises optical detection of the surface defects on any patterned surfaces. Preprints or tactile writing applied in printing or laser processes, for example, have a disruptive effect, since they are usually more visible than the surface defects to be detected themselves, so that these may be detected as pseudo defects.

Hence, such areas are usually statically unmasked, i. statically removed from the inspection area. However, this is often unacceptable under real conditions, especially when the preprints or tactile fonts change dynamically from document to document. When inspecting personalized identification documents, the preprints and tactile fonts are different, for example on each identification document. In addition, the position of any surface defects is typically unknown in advance, which means that these cannot be statically unmasked either.

It is therefore an object of the present invention to create an efficient concept for detecting a surface defect of an identification document.

This object is achieved by the features of the independent claims. Advantageous forms of further development are the subject matter of the dependent claims, the description and the drawings.

The invention is based on the knowledge that the above object can be achieved by a device which illuminates a surface of an identification document with directed light and captures an image of the identification document, the image of the identification document having an inhomogeneity which indicates the surface defect. The inhomogeneity is shown, for example, in that it stands out against a homogeneous background in the image. Such an inhomogeneity can be present, for example, in the form of an image segment and can be detected by means of known image segmentation approaches. The illumination of the surface of the identification document and the acquisition of the image can each take place at a flat angle between 15 ° and 20 ° to the surface, whereby preprints on typical identification documents are no longer visible in the image.

The identification document can be, for example, one of the following identification documents: identity document, such as ID card, passport, access control ID, authorization ID, company ID, tax code or ticket, birth certificate, driver's license or vehicle ID, means of payment such as a bank card or credit card. The identification document can have one or more layers or be paper and / or plastic-based.

According to a first aspect, the invention relates to a device for detecting a surface defect of an identification document, the surface defect being arranged on a surface of the identification document. The device comprises a light source which is designed to emit directed light in the direction of the surface of the identification document, the directed light being reflected on the surface of the identification document. The device further comprises a camera which is designed to detect the reflected light from the surface of the identification document in order to obtain an image of the identification document, the image of the identification document having an inhomogeneity which indicates the surface defect. The device further comprises a detection device which is designed to determine a position of the inhomogeneity in the image of the identification document in order to detect the surface defect of the identification document.

According to one embodiment, a first optical axis of the light source and the surface of the identification document enclose a first angle which is smaller than 90 °, and a second optical axis of the camera and the surface of the identification document enclose a second angle which is smaller than 90 ° is. This has the advantage that the visibility of the surface defect in the image of the identification document can be improved.

According to one embodiment, the first angle lies in a first angle range between 15 ° and 20 °, and the second angle lies in a second angle range between 15 ° and 20 °. This has the advantage that preprints on typical identification documents are no longer visible in the image. In particular, the surface of the identification document can be reflective appear, whereby the position of the inhomogeneity, which indicates the surface defect, can be determined particularly easily.

According to one embodiment, the first angle and the second angle are the same. This has the advantage that the directed or reflected light can be used particularly efficiently.

According to one embodiment, the device comprises a mirror which is arranged and designed to deflect the reflected light from the surface of the identification document to the camera. This has the advantage that the mutual arrangement and alignment of the light source and the camera can be simplified.

According to one embodiment, the detection device is designed to determine a position of the identification document relative to the camera and to rectify the perspective of the image of the identification document on the basis of the determined position. This has the advantage that the position of the inhomogeneity in the image of the identification document can be determined particularly efficiently.

According to one embodiment, the detection device is designed to determine at least one edge in the image of the identification document, the at least one edge pointing to at least one edge of the identification document, and to determine the position of the identification document relative to the camera on the basis of the at least one edge . This has the advantage that the position of the identification document relative to the camera can be determined particularly efficiently.

According to one embodiment, the image of the identification document has a plurality of image pixels, the detection device being designed to determine an average value of at least two color values of at least two adjacent image pixels in order to obtain an average color value, and the average color value of the at least two adjacent image pixels assign. This has the advantage that the image of the identification document can be efficiently preprocessed. In particular, the visibility of any forms of the identification document can be further reduced.

According to one embodiment, the detection device is designed to determine an image segment with a plurality of image segment pixels in the image of the identification document, the image segment representing the inhomogeneity in the image of the identification document. This has the advantage that the position of the inhomogeneity can be determined particularly easily. The image segment can be captured using known image segmentation approaches.

According to one embodiment, the detection device is designed to determine a color value of the plurality of image segment pixels and to assign the image segment to the surface defect of the identification document if the determined color values of the plurality of image segment pixels are within a predetermined reference color value range. This has the advantage that the assignment of the image segment to the surface defect can take place more reliably.

According to one embodiment, the detection device is designed to determine a number of image segment pixels of the image segment and to assign the image segment to the surface defect of the identification document if the determined number of image segment pixels exceeds a predetermined reference number. This has the advantage that the assignment of the image segment to the surface defect can take place more reliably.

According to one embodiment, the image of the identification document is a gray value image. This has the advantage that the position of the inhomogeneity in the image of the identification document can be determined particularly easily.

According to one embodiment, the device comprises a print inspection device which is designed to unmask the surface defect of the identification document in the image of the identification document in order to obtain an unmasked image of the identification document, and to carry out a print inspection of the identification document on the basis of the unmasked image and a pre-stored reference image . This has the advantage that the surface defect is not detected as a pseudo-defect during the print inspection.

According to one embodiment, the print inspection device is designed to determine a deviation measure between a color value of an image pixel of the unmasked image and a reference color value of a reference image pixel of the reference image, and to carry out the print inspection of the identification document further on the basis of the deviation measure. This has the advantage that the print inspection can be carried out particularly efficiently.

According to one embodiment, the surface defect of the identification document is one of the following surface defects: a scratch on the surface of the identification document, a contamination on the surface of the identification document, a fiber on the surface of the identification document, a film residue on the surface of the identification document, a paint residue on the surface of the identification document. This has the advantage that typical surface defects which occur during the production of identification documents can be detected.

According to a second aspect, the invention relates to a method for operating a device for detecting a surface defect of an identification document, the surface defect being arranged on a surface of the identification document. The device comprises a light source, a camera, and a detection device. The method comprises emitting directed light in the direction of the surface of the identification document by the light source, wherein the directed light is reflected on the surface of the identification document, detecting the reflected light from the surface of the identification document by the camera in order to produce an image of the identification document obtained, wherein the image of the identification document has an inhomogeneity which indicates the surface defect, and determining a position of the inhomogeneity in the image of the identification document by the detection device in order to detect the surface defect of the identification document.

The method can be carried out by the device. Further features of the method result directly from the features and / or the functionality of the device.

According to a third aspect, the invention relates to a computer program with a program code for executing the method when the program code is executed by a device.

The device, in particular the detection device, can be set up in terms of programming to execute the program code.

The invention can be implemented in hardware and in software.

• 1 ein schematisches Diagramm einer Vorrichtung zum Erfassen eines Oberflächendefekts eines Identifikationsdokumentes;
• 2 ein schematisches Diagramm eines Verfahrens zum Betreiben einer Vorrichtung zum Erfassen eines Oberflächendefekts eines Identifi kationsdokumentes;
• 3a ein schematisches Diagramm einer Vorrichtung zum Erfassen eines Oberflächendefekts eines Identifikationsdokumentes;
• 3b ein schematisches Diagramm einer Vorrichtung zum Erfassen eines Oberflächendefekts eines Identifikationsdokumentes;
• 3c ein schematisches Diagramm einer Vorrichtung zum Erfassen eines Oberflächendefekts eines Identifikationsdokumentes;
• 4 ein schematisches Diagramm eines perspektivisch verzerrten Bildes eines Identifi kationsdokumentes;
• 5 ein schematisches Diagramm eines perspektivisch entzerrten Bildes eines Identifikationsdokumentes bei Beleuchtung durch eine Lichtquelle mit gerichtetem Licht;
• 6 ein schematisches Diagramm eines perspektivisch entzerrten weiteren Bildes eines Identifikationsdokumentes bei Beleuchtung durch eine weitere Lichtquelle mit diffusem Licht;
• 7 ein schematisches Diagramm einer Demaskierungsmaske eines Identifikationsdokumentes zur Druckinspektion;
• 8 ein schematisches Diagramm eines demaskierten Bildes eines Identifikationsdokumentes zur Druckinspektion; und
• 9 ein schematisches Diagramm eines perspektivisch entzerrten Bildes eines Identifikationsdokumentes bei Beleuchtung durch eine Lichtquelle mit gerichtetem Licht sowie eines demaskierten Bildes des Identifi kationsdokumentes.

Further embodiments are explained in more detail with reference to the accompanying drawings. Show it:

• 1 a schematic diagram of an apparatus for detecting a surface defect of an identification document;
• 2 a schematic diagram of a method for operating an apparatus for detecting a surface defect of an identification document;
• 3a a schematic diagram of an apparatus for detecting a surface defect of an identification document;
• 3b a schematic diagram of an apparatus for detecting a surface defect of an identification document;
• 3c a schematic diagram of an apparatus for detecting a surface defect of an identification document;
• 4th a schematic diagram of a perspective distorted image of an identification document;
• 5 a schematic diagram of a perspective rectified image of an identification document when illuminated by a light source with directed light;
• 6th a schematic diagram of a perspective rectified further image of an identification document when illuminated by a further light source with diffuse light;
• 7th a schematic diagram of an unmasking mask of an identification document for print inspection;
• 8th a schematic diagram of an unmasked image of an identification document for print inspection; and
• 9 a schematic diagram of a perspective rectified image of an identification document when illuminated by a light source with directed light and an unmasked image of the identification document.

1 Figure 3 shows a schematic diagram of an apparatus 100 for detecting a surface defect of an identification document, wherein the surface defect is arranged on a surface of the identification document.

The device 100 includes a light source 101 which is designed to emit directed light in the direction of the surface of the identification document, the directed light being reflected on the surface of the identification document. The device 100 also includes a camera 103 which is designed to detect the reflected light from the surface of the identification document in order to obtain an image of the identification document, the image of the identification document having an inhomogeneity which indicates the surface defect. The device 100 further comprises a detection device 105 , which is formed, a position of the inhomogeneity in the image of the To determine identification document in order to detect the surface defect of the identification document. The device 100 can also include a pressure inspection device 107 which is designed to unmask the surface defect of the identification document in the image of the identification document in order to obtain an unmasked image of the identification document, and to carry out a print inspection of the identification document on the basis of the unmasked image and a pre-stored reference image.

2 Figure 3 shows a schematic diagram of a method 200 for operating a device for detecting a surface defect of an identification document, the surface defect being arranged on a surface of the identification document. The device comprises a light source, a camera, and a detection device.

The procedure 200 includes sending out 201 detecting directed light in the direction of the surface of the identification document by the light source, the directed light being reflected on the surface of the identification document 203 of the reflected light from the surface of the identification document by the camera to obtain an image of the identification document, wherein the image of the identification document has an inhomogeneity which indicates the surface defect, and a determination 205 a position of the inhomogeneity in the image of the identification document by the detection device in order to detect the surface defect of the identification document.

3a Figure 3 shows a schematic diagram of an apparatus 100 for detecting a surface defect of an identification document 301 , wherein the surface defect is on a surface of the identification document 301 is arranged.

The device 100 includes a light source 101 which is designed to produce directional light 303a in the direction of the surface of the identification document 301 to send out, the directional light 303a on the surface of the identification document 301 is reflected. The device 100 also includes a camera 103 , which is formed, the reflected light 303b from the surface of the identification document 301 to capture an image of the identification document 301 to obtain the image of the identification document 301 has an inhomogeneity, which indicates the surface defect. The device 100 furthermore comprises a detection device (not shown) which is designed to determine a position of the inhomogeneity in the image of the identification document 301 to determine the surface defect of the identification document 301 capture.

The device 100 may further comprise a print inspection device (not shown) which is designed to detect the surface defect of the identification document 301 in the image of the identification document 301 to unmask to unmask an image of the identification document 301 and a print inspection of the identification document 301 to be carried out on the basis of the unmasked image and a pre-stored reference image.

In the device shown 100 illuminates the light source 101 the surface of the identification document 301 at a shallow angle, which creates a shadow on the surface defect and can be made visible in the image.

The optical axis of the camera 103 stands, for example, perpendicular to the surface of the identification document 301 so that no perspective distortion occurs. The device shown 100 allows the detection of the surface defect, especially in the case of homogeneous surfaces without pronounced pre-pressures, since an existing pre-pressure would superimpose the surface defect to be detected. In particular, the form can continue to be visible next to the surface defect.

3b and 3c each show a schematic diagram of an apparatus 100 for detecting a surface defect of an identification document 301 , wherein the surface defect is on a surface of the identification document 301 is arranged.

The device 100 includes a light source 101 which is designed to produce directional light 303a in the direction of the surface of the identification document 301 to send out, the directional light 303a on the surface of the identification document 301 is reflected. The device 100 also includes a camera 103 , which is formed, the reflected light 303b from the surface of the identification document 301 to capture an image of the identification document 301 to obtain the image of the identification document 301 has an inhomogeneity, which indicates the surface defect. The device 100 furthermore comprises a detection device (not shown) which is designed to determine a position of the inhomogeneity in the image of the identification document 301 to determine the surface defect of the identification document 301 capture. The in 3c shown device 100 additionally a mirror 307 , which is arranged and formed, the reflected light 303b of the Surface of the identification document 301 to the camera 103 redirect. In the device 100 close a first optical axis of the light source 101 and the surface of the identification document 301 a first angle which is smaller than 90 °, and enclose a second optical axis of the camera 103 and the surface of the identification document 301 a second angle which is smaller than 90 °. The first angle lies, for example, in a first angle range between 15 ° and 20 °, and the second angle lies, for example, in a second angle range between 15 ° and 20 °.

The device 100 further comprises a further light source 305 , which is formed, diffuse light in the direction of the surface of the identification document 301 to send out.

The device 100 may further comprise a print inspection device (not shown) which is designed to detect the surface defect of the identification document 301 in the image of the identification document 301 to unmask to unmask an image of the identification document 301 and a print inspection of the identification document 301 to be carried out on the basis of the unmasked image and a pre-stored reference image.

In the device shown 100 the light source is arranged 101 and the camera 103 each other in reflection. The light source 101 illuminates the surface of the identification document 301 at a flat angle, for example between 15 ° and 20 °, whereby a shadow is formed on the surface defect and can be made visible. The camera 103 records the identification document to be inspected 301 for example at the same angle. An optical axis of the camera can be used 103 placed directly at this angle (see 3b) . Alternatively, the reflected light 303b over the mirror 307 for the purpose of optical path extension or for the purpose of easier camera positioning (see 3c ). Both possibilities are equivalent.

Due to the inclined arrangement of the camera 103 relative to the identification document 301 the captured image is typically distorted in perspective. However, this can be corrected again by a perspective rectification. Mainly the surface defect remains visible, while any existing pre-pressures can become invisible. The surface of the identification document 301 can appear “mirrored” in the captured image. Existing tactile security features can remain easily visible; however, they can be dynamically removed from the inspection area by later unmasking.

The further light source, for example, can be used to unmask tactile security features 305 be used, which is designed to emit diffuse light in the direction of the surface of the identification document. The other light source 305 allows the already existing tactile security elements to be illuminated. Typical surface defects are in the illumination by the additional light source 305 not visible. The other light source 305 can emit diffuse light in an infrared (IR) wavelength range, for example.

4th shows a schematic diagram of a perspective distorted image of an identification document 301 . The image is due to the arrangement of the camera relative to the identification document 301 distorted perspective.

Over the four edges of the identification document 301 which can be detected, for example, by means of the indicated 8 points of a perspective distorted rectangle, the parameters for the perspective rectification can be determined.

5 shows a schematic diagram of a perspective rectified image of an identification document 301 when illuminated by a light source with directed light (left) in comparison with a reference image of an identification document 301 (right).

In the case of the perspective rectified image, there are preprints on the identification document 301 , for example fine line patterns (guilloches), no longer visible. Only any surface defects remain visible on the surface of the identification document 301 and possibly tactile security features, for example tactile writing.

In the reference image, however, the fine line patterns (guilloches) are clearly visible.

6th shows a schematic diagram of a perspective rectified further image of an identification document 301 when illuminated by another light source with diffuse light. The further light source can, for example, emit diffuse light in an infrared (IR) wavelength range.

The further image can be used, for example, for tactile security features on the surface of the identification document 301 to capture and unmask.

7th shows a schematic diagram of an unmasking mask of an identification document 301 for print inspection. The white areas represent unmasked areas which are left out during the print inspection. In the unmasking mask shown, both surface defects and tactile security features of the identification document are unmasked by way of example.

The unmasking of texts can be based on a corresponding image segmentation. The unmasking of images can be based on a corresponding edge detection in order to reduce the area of the unmasked area.

8th Figure 3 shows a schematic diagram of an unmasked image of an identification document 301 for print inspection. The light areas represent unmasked areas that are used for print inspection.

A non-unmasked area is shown on the left, which is used for texts. On the right is a non-unmasked area that is used for photos. The distinction between the text area and the photo area can be made, for example, because inspection parameters can thus be determined more precisely depending on the type of area to be inspected.

Alternatively or additionally, the further image can be unmasked in order to obtain a further unmasked image. The print inspection can alternatively or additionally be carried out using the unmasked further image.

9 shows a schematic diagram of a perspective rectified image of an identification document 301 when illuminated by a light source with directed light and an unmasked image of the identification document 301 .

In both images, exemplary surface defects in the form of scratches and small amounts of dirt are highlighted.

The device 100 as well as the procedure 200 consequently enable an inspection of the surface of the identification document 301 , whereby a reliable and robust detection of surface defects such as scratches or contamination can be carried out even on randomly patterned, inhomogeneous surfaces. Existing pre-pressures on the surface or tactile security features, in addition to the surface defects, can be eliminated. In particular, the light source 101 relative to the camera 103 be arranged in reflection. In addition, tactile security features can be detected using the further light source 305 respectively. This allows dynamic unmasking of the captured images. In addition, pre-pressures with particularly strong contrast transitions can be recorded.

The light source 101 can illuminate the surface to be inspected at a flat angle, for example between 15 ° and 20 °, in order to make the surface defects visible through a shadow effect. The camera 103 can view the surface at the same angle, i.e. the camera 103 can detect the light reflected from the surface. With this arrangement, surface defects become visible, while any preprinted patterns can disappear. Only existing tactile security features or very high-contrast transitions in the form can remain partially visible. However, these can be separated using the additional light source 305 capture and dynamically unmask.

The other light source 305 , which is formed, diffuse light in the direction of the surface of the identification document 301 to send out enables illumination of the surface of the identification document 301 to determine the tactile security features to be unmasked.

Depending on the type of tactile security feature, diffuse light from an infrared (IR) wavelength range or a whitish wavelength range can be used, for example. For example, diffuse light from the infrared (IR) wavelength range can be used to illuminate lasered content and diffuse light from the whitish wavelength range can be used to illuminate printed content. When illuminated with diffuse light, surface defects such as scratches are typically not visible.

Once the tactile security features or high-contrast transitions are visible, they can be found and unmasked, for example, by means of corresponding image segmentation or by means of corresponding edge detection, so that as little pseudo errors as possible are detected. Typically, only small or minimal areas are unmasked in comparison to static unmasking.

• Zunächst erfolgt eine Erfassung eines Bildes des Identifikationsdokumentes 301 bei Beleuchtung mit der Lichtquelle 101, welche gerichtetes Licht aussendet. Es erfolgt eine perspektivische Entzerrung des erfassten Bildes, welche durch die schräge Anordnung der Kamera 103 zu dem Identifikationsdokument 301 entsteht. Dabei wird die Form des Identifikationsdokumentes 301 in dem Bild von einem Trapez zurück auf ein Rechteck abgebildet. Die Oberflächeninspektion soll typischerweise auf Grundlage des perspektivisch entzerrten Bildes erfolgen.

A print inspection using the light source 101 and / or the further light source 305 can be done, for example, as follows:

• First, an image of the identification document is captured 301 when illuminated with the light source 101 which emits directional light. A perspective rectification of the captured image takes place, which is caused by the inclined arrangement of the camera 103 to the identification document 301 arises. The form of the identification document 301 in the picture from a trapezoid back to a rectangle. The surface inspection should typically take place on the basis of the perspective rectified image.

Based on the known rectangular shape of the identification document 301 and the previously known size of the identification document, the parameters for the perspective rectification or transformation can be determined. For this purpose, for example, 8 points can be placed on the edges of the identification document 301 to be determined. The perspective rectification of the image can then take place using a direct linear transformation (DLT: Direct Linear Transform) and an associated linear equation system. Due to the perspective rectification of the image, in particular a metrically correct inspection of the surface can be realized.

A further image of the identification document is then recorded 301 when illuminated by the additional light source 305 which emits diffuse light. Furthermore, a perspective rectification of the further image can take place.

Through the illumination by means of the additional light source 305 can tactile security features on the surface of the identification document 301 are recorded. Furthermore, the tactile security features can be unmasked. The inclined arrangement of the camera 103 to the identification document 301 can also be compensated here by means of a perspective rectification. The same approach as described above can be used.

Then the unmasking takes place. The visible tactile security features, for example tactile writing, or high-contrast transitions are dynamically recorded and unmasked in the image and / or the further image. For areas with texts, i.e. fine lines and smaller areas, an appropriate image segmentation can be used to determine the unmasked areas. In the case of photos, it is possible to find strongly pronounced edges with a magnification factor as the unmasked area, so that the area of the unmasking is smaller.

For example, the image and / or the further image can be unmasked and the print inspection can be carried out on the basis of the image and / or the further image. During the print inspection, the image and / or the further image can, for example, each be compared with a pre-stored reference image.

A homogeneity test can be carried out in this case, with defective pixels being identified within the inspection area. The inspection area is checked for homogeneity, for example, i.e. Image pixels that deviate from the homogeneous environment can be marked as defective pixels. For this purpose, the inspection area can, for example, be broken down into grid cells with adjacent image pixels. For example, a mean value of the gray values can be calculated within each grid cell. Image pixels that deviate too much from the mean gray value (local segmentation) or image pixels that lie outside a global segmentation interval (global segmentation) can be marked as defective pixels.

In addition, an area analysis can be carried out, with the area analysis being able to combine those defect pixels into defect areas that were identified in the previous step. According to this, different metric tolerance values, such as an area length, an area area of individual defect areas, or a total area of the areas for defects can be specified, which define from when a recognized defect should actually be accepted as such.

In summary, an inspection of patterned surfaces of identification documents is made possible, which can change dynamically.

The quality control in the production of identity documents can consequently be extended to many applications in practice, whereby there is no restriction to homogeneous surfaces without pre-prints.

All features described or shown in connection with individual embodiments can be provided in any combination in the subject matter according to the invention in order to simultaneously realize their advantageous effects.

List of reference symbols

100

contraption

101

Light source

103

camera

105

Detection device

107

Pressure inspection device

200

Procedure

201

Send out

203

Capture

205

Determine

301

Identification document

303a

Directed light

303b

Reflected light

305

More light source

307

mirror

Claims (15)

Device (100) for detecting a surface defect of an identification document (301), wherein the surface defect is arranged on a surface of the identification document (301), with: a light source (101) which is designed to emit directed light (303a) in the direction of the surface of the identification document (301), the directed light (303a) being reflected on the surface of the identification document (301); a camera (103) which is designed to capture the reflected light (303b) from the surface of the identification document (301) in order to obtain an image of the identification document (301), the image of the identification document (301) having an inhomogeneity, which indicates the surface defect; and a detection device (105) which is designed to determine a position of the inhomogeneity in the image of the identification document (301) in order to detect the surface defect of the identification document (301). Device (100) after Claim 1 , wherein a first optical axis of the light source (101) and the surface of the identification document (301) enclose a first angle which is smaller than 90 °, and wherein a second optical axis of the camera (103) and the surface of the identification document (301) Include a second angle which is smaller than 90 °. Device (100) after Claim 2 , where the first angle and the second angle are the same. Device (100) according to one of the preceding claims, comprising: a mirror (307) which is arranged and designed to deflect the reflected light (303b) from the surface of the identification document (301) to the camera (103). Device (100) according to one of the preceding claims, wherein the detection device (105) is designed to determine a position of the identification document (301) relative to the camera (103) and the image of the identification document (301) on the basis of the determined position to rectify perspective. Device (100) after Claim 5 , wherein the detection device (105) is designed to determine at least one edge in the image of the identification document (301), wherein the at least one edge indicates at least one edge of the identification document (301), and the position of the identification document (301) relative to of the camera (103) on the basis of the at least one edge. Device (100) according to one of the preceding claims, wherein the image of the identification document (301) has a plurality of image pixels, and wherein the detection device (105) is designed to determine a mean value of at least two color values of at least two adjacent image pixels to determine one to obtain averaged color value, and to assign the averaged color value to the at least two adjacent image pixels. Device (100) according to one of the preceding claims, wherein the detection device (105) is designed to determine an image segment with a plurality of image segment pixels in the image of the identification document (301), and wherein the image segment shows the inhomogeneity in the image of the identification document (301 ) represents. Device (100) after Claim 8 , wherein the detection device (105) is designed to determine a color value of the plurality of image segment pixels, and to assign the image segment to the surface defect of the identification document (301) if the determined color values of the plurality of image segment pixels are within a predetermined reference color value range. Device (100) according to one of the Claims 8 or 9 , wherein the detection device (105) is designed to determine a number of image segment pixels of the image segment, and to assign the image segment to the surface defect of the identification document (301) if the specific number of image segment pixels exceeds a predetermined reference number. Device (100) according to one of the preceding claims, wherein the image of the identification document (301) is a gray value image. Device (100) according to one of the preceding claims, comprising: a print inspection device (107) which is designed to unmask the surface defect of the identification document (301) in the image of the identification document (301) in order to obtain an unmasked image of the identification document (301), and a print inspection of the identification document (301) on the Perform based on the unmasked image and a pre-stored reference image. Device (100) according to one of the preceding claims, wherein the surface defect of the identification document (301) is one of the following surface defects: a scratch on the surface of the identification document (301), a contamination on the surface of the identification document (301), a fiber on the Surface of the identification document (301), a film residue on the surface of the identification document (301), a paint residue on the surface of the identification document (301). Method (200) for operating a device (100) for detecting a surface defect of an identification document (301), wherein the surface defect is arranged on a surface of the identification document (301), the device (100) having a light source (101), a camera ( 103), and a detection device (105) comprising: Emitting (201) directed light (303a) in the direction of the surface of the identification document (301) by the light source (101), the directed light (303a) being reflected on the surface of the identification document (301); Detection (203) of the reflected light (303b) from the surface of the identification document (301) by the camera (103) in order to obtain an image of the identification document (301), the image of the identification document (301) having an inhomogeneity which can be indicates the surface defect; and Determining (205) a position of the inhomogeneity in the image of the identification document (301) by the detection device (105) in order to detect the surface defect of the identification document (301). Computer program with a program code for carrying out the method (200) according to Claim 14 when the program code is executed by a device (100).

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