US 11,930,147 B2
System and method for automatic identification of photocopied documents
Armando Munoz Utiel, Madrid (ES); and David Gonzalez Garcia, Madrid (ES)
Assigned to SOTEC CONSULTING S.L., Madrid (ES)
Appl. No. 17/277,413
Filed by SOTEC CONSULTING S.L., Madrid (ES)
PCT Filed Sep. 26, 2018, PCT No. PCT/ES2018/070620
§ 371(c)(1), (2) Date Mar. 18, 2021,
PCT Pub. No. WO2020/065101, PCT Pub. Date Apr. 2, 2020.
Prior Publication US 2022/0038599 A1, Feb. 3, 2022
Int. Cl. H04N 1/32 (2006.01); B42D 25/333 (2014.01); B42D 25/387 (2014.01)
CPC H04N 1/3216 (2013.01) [B42D 25/333 (2014.10); B42D 25/387 (2014.10); H04N 1/32203 (2013.01)] 16 Claims
OG exemplary drawing
 
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.