Why Do Some Printers Have Secret Tracking Dots?

Have you ever encountered a common printer problem where your printer absolutely insists on having colored ink available, even if you're only printing in black and white? It's not because it's trying to coerce you into replacing your old recycled ink cartridges, but rather, it's because everything you've been printing with that printer has been subtly dotted with distinctive colored tracking dots. These dots, which are in a shade invisible to the naked eye, serve as a subtle identification system indicating where a print came from and when it was printed.

Most color printers from the most reliable brands use this tracking dot system, placing a network of tiny dots on every document you print, even if you tell them to use only black and white ink. These dots can be read by someone familiar with a manufacturer's encoding system to determine the precise make and model of your printer, the date and time you used it, and, in some cases, whether you were printing a document alone or copying another one. This practice has roots in both encoded messages sent during World War II and counterfeit-prevention measures used on banknotes.

If you take a close look at any document printed off from your color printer, either with a microscope or under special lighting, you would see a multitude of dots arranged in a grid-like configuration. These dots are printed in an extremely light shade of yellow that you can't see with the naked eye, but they're definitely there. Your printer adds these dots during every print job, with their layout in the grid serving as identifying markers. These markers, also known as Machine Identification Codes, serve as a digital fingerprint for your printer. By analyzing the markers, along with knowledge of a manufacturer's encoding practices, you could get a complete readout of the document's printer of origin, as well as the exact day and time it was printed.

There is no publicly stated reason why printer manufacturers add this feature, but the consensus is that it's to help forensic investigators detect forgeries, in a similar vein to the microscopic dots placed on banknotes. A random person could print off a document and say they got it from a specific source or individual a long time ago, for example, but consulting the tracking dots would reveal that it came from their own printer last week, challenging their claim. In fact, the earliest color printers produced by Xerox in the 1980s specifically used this system, so they couldn't be used to forge banknotes.