Remember the Brady Bunch episode where the family traces a letter from Jan's "secret admirer" to Alice's typewriter? Of course you remember it. Now, researchers at Purdue University have developed a similar technique for laser printers. Law enforcement would use the approach to bust counterfeiters and forgers.
The technique uses specialized software to detect slight variations, or "intrinsic signatures," of printed characters, revealing subtle differences from one printer to another. Even printers that are the same model have slight flaws and variations in their mechanical systems. These variations result in subtly different characters.Link (via Slashdot)
"We have observed variability from printer to printer within a single model, " (researcher Jan) Allebach said. "That’s because for a company to make printers all behave exactly the same way would require tightening the manufacturing tolerances to the point where each printer would be too expensive for consumers.