Forensic Identification
Alike to forensic identification of typewriters, computer printers and copiers can be traced by flaws in their output. The mechanical tolerances of the toner and paper feed mechanisms cause banding, which can disclose information about the individual device's mechanical properties. It is often possible to recognize the manufacturer and brand, and, in some cases, the individual printer can be recognized from a set of known printers by comparing their outputs.
Some high-quality color printers and copiers steganographically embed their identification code into the printed pages, as fine and almost invisible patterns of yellow dots. The Electronic Frontier Foundation (EFF) has investigated this issue and documented how the Xerox DocuColor printer's serial number, as well as the date and time of the printout, are encoded in a repeating 8×15 dot pattern in the yellow channel. EFF is working to reverse engineer additional printers. The US government has been reported to have asked these companies to apply such a tracking scheme, so that counterfeiting can be traced.