Every few years or so, the press picks up on the story that laser printers leave some dots that are invisible to the naked eye on every print. These dots are included for the purpose of anti-counterfeiting efforts. Each printer leaves a unique mark that can be read with special blue LED light, and interpreted with a decoding system that only the printers and the secret service are supposed to have. The story is getting some press again as the EFF is pointing out that laser printers have become cheap enough that many people have them and it's possible that the identification dots could be used for other purposes
, meaning that people who print stuff out on the assumption that the documents would be anonymous, may be wrong. Officials in the article scoff at the idea that the codes would be used for anything other than anti-counterfeiting efforts. And, indeed, it does seem unlikely that the codes could be used for very much (not only would you need to interpret them, you'd also need the means of tracking down who owns a specific printer). But there is a good point in all of this: why shouldn't the printer providers be forced to at least disclose that their printers mark every document with a unique identifier?