The EFF has broken the tracking code for the Xerox DocuColor. The DocuColor prints a faint 15×8 grid of yellow dots on every page. To see these dots you need a magnifying glass. You can also use a blue light to make the dots appear black. The EFF page has a built in application for decoding the dots which hide the time, date, and serial number of the printer. The EFF also maintains a list of printers which do or don’t have this “feature”.
Andrew “bunnie” Huang helped out a lot with this research. To speed up analysis of submitted printer samples he modified a scanner to use blue light. The scanner does a white balance calibration before each page scan so the blue lights need to be turned off during that period otherwise the scanner will compensate. bunnie also opened up his HP 2600N to determine where the watermark was implemented. Studying the boards he decided that most color laser printers are probably using Canon engine boards. By coercing one manufacturer the government was able to get watermarking into a majority of the laser printers sold.