CPC H04N 1/3216 (2013.01) [B42D 25/333 (2014.10); B42D 25/387 (2014.10); H04N 1/32203 (2013.01)] | 16 Claims |
1. A method for automatic identification of photocopied documents, comprising:
capturing an image of a marked printed document with a digital watermark;
obtaining, from the captured image, a calibration identifier;
recovering, by searching a database, a calibration threshold associated with the calibration identifier;
applying a discrete Fourier transform to the image, obtaining a frequency matrix;
converting the frequency matrix to a logarithmic scale;
binarizing the matrix converted to a logarithmic scale, so that the matrix values above a predetermined binarization threshold correspond to frequency maximums;
measuring the area, defined in number of pixels, of the frequency maximums that appear in the binarized frequency matrix, obtaining a maximum frequency value for each frequency maximum;
comparing the maximum frequency value of each frequency maximum with the calibration threshold;
determining, on the basis of the comparison, if the marked printed document is an original document or a photocopied document.
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