Method for verifying a valuable document having a polymer substrate and a transparent window and means for carrying out said method

1. A method for checking a value document for the presence of print removals, said value document having a polymer substrate and at least one see-through window, the method comprising the steps of:

capturing a digital transmission image of the value document, the transmission image comprising pixels;

ascertaining in the image an edge brightness value that indicates the brightness of an edge of the at least one see-through window;

using the edge brightness value, ascertaining a threshold value for the brightness of pixels, said threshold value being suited to determine whether there is an indication of the presence of a print removal, said threshold being smaller than the edge brightness value but greater than the minimal brightness in the image;

searching pixels which lie in at least one specified portion of the image and outside the at least one see-through window and its edge and have a brightness which lies above the threshold value; and

in dependence of the result of the searching, forming at least one signal and/or storing at least one datum which represents the result of the searching.

2. The method according to claim 1 , wherein the digital transmission image is a digital infrared transmission image.

3. The method according to claim 1 , further comprising the step of ascertaining an edge brightness value the maximum of the brightnesses of the pixels of the whole transmission image.

4. The method according to claim 1 , further comprising the steps of:

ascertaining a region of the image showing the see-through window with its edge; and

employing as an edge brightness value the mean value or the maximum of the brightnesses of at least two of the pixels of at least the edge of the image of the see-through window, or

ascertaining the maximum of the brightnesses of the region of the image; and

employing the mean value or the maximum of the brightnesses of the region of the image as an edge brightness value.

5. The method according to claim 4 , wherein the specified part of the image does not show the edge of the see-through window and the see-through window.

6. The method according to claim 5 , further comprising the step of ascertaining a local distribution of the pixels found upon the search whose brightness lies above the threshold value.

7. The method according to claim 1 , further comprising the step of ascertaining the threshold value such that it is greater than a mean value over the brightnesses of the pixels in at least one specified part of the image or the pixels of the image of the whole value document.

8. The method according to claim 1 , further comprising the step of ascertaining how many pixels were found upon the search.

9. The method according to claim 1 , further comprising the step of ascertaining in dependence on the result of the search in dependence on the number and/or the local distribution of the pixels found upon the search a state value for the value document.

10. An apparatus for checking a value document for the presence of print removals, said value document having a polymer substrate and a see-through window, with

an evaluation device which is configured for executing a method comprising the steps of:

capturing a digital transmission image of the value document, the transmission image comprising pixels;

ascertaining in the image an edge brightness value that indicates the brightness of an edge of the at least one see-through window;

using the edge brightness value, ascertaining a threshold value for the brightness of pixels, said threshold value being suited to determine whether there is an indication of the presence of a print removal, said threshold being smaller than the edge brightness value but greater than the minimal brightness in the image;

searching pixels which lie in at least one specified portion of the image and outside the at least one see-through window and its edge and have a brightness which lies above the threshold value;

in dependence of the result of the searching, forming at least one signal and/or storing at least one datum which represents the result of the searching.

11. The apparatus according to claim 10 , further comprising an optical transmission sensor for capturing a digital transmission image of the value document which is coupled to the evaluation device, and in which the evaluation device is configured to capture an image of the transmission sensor as a digital image.

12. The apparatus according to claim 11 , wherein the optical transmission sensor comprises an optical transmission sensor for capturing a digital transmission image of the value document.

13. A data processing device comprising a physical data carrier which has a program code, upon the execution of which the data processing device executes a method for checking a value document for the presence of print removals, said value document having a polymer substrate and at least one see-through window, the method comprising the steps of:

capturing a digital transmission image of the value document, the transmission image comprising pixels;

ascertaining in the image an edge brightness value that indicates the brightness of an edge of the at least one see-through window;

using the edge brightness value, ascertaining a threshold value for the brightness of pixels, said threshold value being suited to determine whether there is an indication of the presence of a print removal, said threshold being smaller than the edge brightness value but greater than the minimal brightness in the image;

searching pixels which lie in at least one specified portion of the image and outside the at least one see-through window and its edge and have a brightness which lies above the threshold value; and

in dependence of the result of the searching, forming at least one signal and/or storing at least one datum which represents the result of the searching.

14. A physical data carrier which is readable by means of a data processing device and on which a computer program according to claim 13 , is stored.