DocuColor Tracking Dot Decoding Guide This guide is part of the Machine Identification Code Technology project. It explains how to read the date, time, and printer serial number from forensic tracking codes in a Xerox DocuColor color laser printout. This information is the result of research by Robert Lee, Seth Schoen, Patrick Murphy, Joel Alwen, and Andrew "bunnie" Huang. We acknowledge the assistance of EFF supporters who have contributed sample printouts to give us material to study. We are still looking for help in this research; we are asking the public to submit test sheets or join the printers mailing list to participate in our reverse engineering efforts.
The DocuColor series prints a rectangular grid of 15 by 8 miniscule yellow dots on every color page. The same grid is printed repeatedly over the entire page, but the repetitions of the grid are offset slightly from one another so that each grid is separated from the others. The grid is printed parallel to the edges of the page, and the offset of the grid from the edges of the page seems to vary. These dots encode up to 14 7-bit bytes of tracking information, plus row and column parity for error correction. Typically, about four of these bytes were unused (depending on printer model), giving 10 bytes of useful data. Below, we explain how to extract serial number, date, and time from these dots. Following the explanation, we implement the decoding process in an interactive computer program. Because of their limited contrast with the background, the forensic dots are not usually visible to the naked eye under white light. They can be made visible by magnification (using a magnifying glass or microscope), or by illuminating the page with blue instead of white light. Pure blue light causes the yellow dots to appear black. It can be helpful to use magnification together with illumination under blue light, although most individuals with good vision will be able to see the dots distinctly using either technique by itself. <snip> http://www.eff.org/Privacy/printers/docucolor/ You are a subscribed member of the infowarrior list. Visit www.infowarrior.org for list information or to unsubscribe. This message may be redistributed freely in its entirety. Any and all copyrights appearing in list messages are maintained by their respective owners.
