One of the most useful techniques for criminal investigation involving shooting is to compare the gun “fingerprint.” Each gun apparently leaves a unique pattern on the bullet so it is easy to verify whether a bullet came from a particular gun.

With the increasing use of high quality printers in counterfeiting and other types of fraud, Xerox and other printer manufacturers have built-in a similar “fingerprint” technology into some of their printers. According to the story, the printers print faint information in very small yellow dots in the background of printed-out pages, to identify the model and serial number of the printer that printed the page. Of course, it is invisible to the naked eye, but it is there (haven’t tested it personally yet, though.)

Ed Felten at Freedom to Tinker has some questions (with no answers yet) about this scheme:

• Is encryption used, and if so, how?
• Is there a secret key? If yes - who knows it?
• Do they track who buys each printer?

It is clear that privacy advocates are and should be asking these questions. Also, based on the encryption and the key used - how easy it is to spoof this identification string? Depending on the strength of the encryption, this scheme could be quickly beaten and become obsolete - there is not really a point in tracking a number which can easily be spoofed.  I am curious to see how courts react to this and what weight it would be given.