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10/20/2005: Speaking of Technology...
...Crooks and Liars had this post about the potential "Tracking Dot Decoding" system from printers.
Most *interesting* and *peculiar* as to what ARE they tracking? And WHY?"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.
...
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..."
And here's what you can decode:
"Each column is read top-to-bottom as a single byte of seven bits (omitting the first parity bit); the bytes are then read right-to-left. The columns (which we have chosen to number from left to right) have the following meanings:
* 15: unknown (often zero; constant for each individual printer; may convey some non-user-visible fact about the printer's model or configuration)
* 14, 13, 12, 11: printer serial number in binary-coded-decimal, two digits per byte (constant for each individual printer; see below)
* 10: separator (typically all ones; does not appear to code information)
* 9: unused
* 8: year that page was printed (without century; 2005 is coded as 5)
* 7: month that page was printed
* 6: day that page was printed
* 5: hour that page was printed (may be UTC time zone, or may be set inaccurately within printer)
* 4, 3: unused
* 2: minute that page was printed
* 1: row parity bit (set to guarantee an odd number of dots present per row)
The printer serial number is a decimal number of six or eight digits; these digits are coded two at a time in columns 14, 13, 12, and 11 (or possibly just 13, 12, and 11); for instance, the serial number 00654321 would be coded with column values 00, 65, 43, and 21.
[Pictures and diagrams are included to help with the explanation and are most instructive.]
So, Forensically speaking, I guess that should tell ya to NEVER use a printer to commit yer crimes!! Or at least not a Xerox DocuColor color laser printer.
:-)
Karen on 10.20.05 @ 08:08 AM CST
