The Edmondson Blog

I have previously blogged about the EURion Constellation, a pattern of dots printed on bank notes to stop forgery. This has apparently been extended to colour laser printers.

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.
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[T]he measure [was] 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.

Hat tip: Puppa