Thursday, November 03, 2005

Laser Printer Color Dots, and Publius, the thief:

When I was living in a college dorm - way before the invention of the word processor - we appreciated the communal pencil sharpener in the hall near the bulletin board. One day the sharpener disappeared, replaced by a type-written note. (There were electric typewriters in those days, but most people, including this thief, did not have one.) The note explained that the thief had stolen the sharpener for his private use and had no intention of giving it back. It was signed: Publius.

I added a note below his, in which I pointed out all the irregularities in his typewriter. The 'e' printed slightly below the line, there was a bit missing in every 't', and so on. I suggested that we keep an eye on any local typescript and we would soon identify Publius. The Pencil sharpener returned to its place the next day.

Today we have have incredibly high quality, accurately machined laser printers, mass-produced by the million. Surely, if Publius had printed his note on a modern color laser printer, he could have rejoiced in his anonymity while even adding a small naughty picture to his signature. Yet it turns out his printout would not be as anonymous as he thought. Read all about it here at the EFF website. Many color printers sneakily print their serial number (and more) in microdots on both sides of every page they print. Quote:
The U.S. Secret Service admitted that the tracking information is part of a deal struck with selected color laser printer manufacturers, ostensibly to identify counterfeiters. However, the nature of the private information encoded in each document was not previously known. "We've found that the dots from at least one line of printers encode the date and time your document was printed, as well as the serial number of the printer," said EFF Staff Technologist Seth David Schoen.
I can imagine George Orwell shaking his head and saying "Wish I'd thought of that."
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