Update 17/10/2018: According to EFF, modern commercial colour laser printers likely use forensic tracking codes even if the yellow dot method is not employed.
With printers being cheap and in just about every home and office, it would seem the humble, letters-cut-out-of-magazines ransom note is now a thing of the past – print your demands in generic Times New Roman and no one would ever be able to identify you, right? Yeah, not so much.
Just about every printer on the planet leaves a digital footprint – tiny, almost invisible yellow dots on every page they print, featuring information such as the printer’s serial number and a timestamp. To pick up the dots, you’d need a microscope and a blue light.
The information is there for the exact reason you would expect, to make pages traceable. It’s a practice known as digital steganography, which IEEE Xplore define as “the art of inconspicuously hiding data within data”.
The Electronic Frontier Foundation reported that the US government got printer companies to put the codes into their products as a means of tracing and catching counterfeiters, but they also noted “there are no laws to stop the Secret Service from using printer codes to secretly trace the origin of non-currency documents”.
In another piece, EFF made a list of almost 200 printers from 20 printer manufacturers, finding the dots on the vast majority.
Only two manufacturers were found to have no marks, Japanese company OkiDATA, and South Korea’s Samsung.
While a few dozen printers from other manufacturers did not have the dots, EFF pointed out that just because they couldn’t identify them didn’t mean they weren’t present, noting “other forensic marking techniques have been invented”.
They also believed, due to information gleaned via documents received thanks to the freedom of information act, that all major printer manufacturers had cut a deal with the US government to include the information.
All of this is a pretty good explanation for why your printer won’t print in black when you have black ink, but no colour ink.