A forensic marking system and method for identifying the printing device on which a medium was printed. Encoded forensic markings which identify the device but are of low perceptibility to the human eye are superimposed on the printed image. The markings have a color, size, density, and repetition pattern...http://www.google.se/patents/US7002710?utm_source=gb-gplus-sharePatent US7002710 - High reliability forensic color marking system
