Printer steganography

An illustration showing small yellow tracking dots on white paper, generated by a color laser printer.

Another illustration. Right picture illuminated using blue light.

Printer steganography is a type of steganography – "hiding data within data" – produced by laser printers, including Brother, Canon, Dell, Epson, HP, IBM, Konica Minolta, Kyocera, Lanier, Lexmark, Ricoh, Toshiba and Xerox brand color laser printers, where tiny yellow dots are added to each page. The dots are barely visible and contain encoded printer serial numbers and timestamps. Unlike many forms of steganography, the hidden information is not intended to be available from a computer file, but to allow serial number and time of printing to be determined by close examination of a printout.

Color laser printers and copiers appear to be the type mostly involved, the measure being brought in during the 1990s by Xerox and other companies seeking to reassure governments that their printers wouldn't be used for forgery. The identification is by means of a watermark, often using yellow-on-white, embedded in the printout of each page, and in conjunction with other information can be used to identify the printer which was used to print any document originally produced on a wide range of popular printers. It has been reported that monochrome printers and copiers from major manufacturers also include the markings. It may be actual text, or a repeated pattern of dots throughout the page, more easily visible under blue light or with a magnifying glass, and is intended to produce minimal visible change to the printout, ideally being imperceptible to the naked eye.

In 2005, the Electronic Frontier Foundation cracked the codes for Xerox DocuColor printers and published an online guide to their detection. Most printers' codes have not been decoded, although the coding system framework and printer serial number encoding is the same on both DocuColor and the Epson Aculaser C1100/C1100N/A.

See also

• Steganography
• Microprinting
• Coded Anti-Piracy
• EURion constellation
• Mobile phone tracking

External links

• Risks-L digest (October 26, 2005)
• DocuColor Tracking Dot Decoding Guide Electronic Frontier Foundation (October, 2005)
• Electronic Frontier Foundation information pages
• Electronic Frontier Foundation list of affected and non affected printers