On Nov. 22, 2004, PC World published an online article entitled “Government Uses Color Laser
Printer Technology to Track Documents,” which stated that “several printer companies quietly
encode the serial number and the manufacturing code of their color laser printers and color
copiers on every document those machines produce. Governments, including the United States,
already use the hidden markings to track counterfeiters.” The article quoted Lorelei Pagano, a
counterfeiting specialist at the Secret Service, as saying that the markings are used only to
investigate counterfeiting cases: “The only time any information is gained from these documents
is purely in [the case of] a criminal act.”
EFF’s research indicates that Xerox and Canon color laser printers, among others, mark
documents with minuscule yellow dots invisible to the unaided human eye, the arrangement of
which likely encodes information such as a machine’s serial number and manufacturer’s name.
On documents printed by Xerox printers, the markings consisted of yellow dots arranged in a 0.5
inch by 1.0 inch rectangular space. The arrangement of dots was repeatedly printed over an
entire page. On documents printed by Canon printers, the markings also consisted of tiny yellow
dots, but they were not arranged within a rectangular space. At first glance, the dots appear to be
without rigid structure, but close examination reveals that they are merely arranged within a non-
rectangular polygon. Since these yellow dots are small and blend easily with a white paper
background, the unaided eye cannot distinguish the dots from the background. |