Printer steganography

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

Printer steganography is a type of steganography produced by color printers, including HP 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, as well as date and time stamps.

Color laser printers appear to be the type mostly involved, the measure being brought in during the 1990s by companies such as Xerox seeking to reassure governments that their printers would not be used for the purposes of 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 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 be very difficult to notice with the naked eye.

In 2005, the Electronic Frontier Foundation cracked the codes for DocuColor printers and published an online guide to their detection.^[1] Most printers' codes have not been decoded.