When you print on certain (all?) colour laser printers it appears the manufacturer of your printer may have secretively built in a way for tracking a document back to you. I guess if someone is printing counterfeit money this could be useful however this sort of tracking is also somewhat creepy.
The Electronic Frontier Foundation (EFF) has decoded the scheme with explanation of how the coding is implemented. Have a read, it’s pretty interesting from the perspective of how they decoded it to how the tracking information is encoded.
