System and method for automatic identification of photocopied documents

A system for automatic identification of photocopied documents, comprising:

• an image acquisition device configured for capturing an image of a marked printed document with a digital watermark;
• a photocopied document identification device comprising a data processing unit configured for:
• receiving the image captured by the image acquisition device;
• obtaining, from the 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;
• binarising the matrix converted to a logarithmic scale, so that the matrix values above a certain binarisation threshold correspond to frequency maximums;
• measuring the area, defined in number of pixels, of the frequency maximums that appear in the binarised 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.