Patent ID: 11930147
Assignee: SOTEC CONSULTING S.L.
Field: Audio-visual technology (Electrical engineering)
Classification: CPC G  H  B | IPC B  H

Claim 0:
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.