Unveiling the Secret Yellow Printer Dots with the Eyeclops Bionic Eye


I used to have a great job as a pre-press tech at a small print shop.

This operation, like other small print shops, used a giant color laser printer, about the size of a Honda limousine.

One day, Tim, the boss, introduced me to the secret, invisible marks that our printer was fusing to every sheet that came out of the printer: The marks were designed to help prevent people from printing high-quality counterfeit money.

A pattern of tiny yellow dots, printed across the page, in a cryptic grid pattern.

On a white sheet of paper, with the naked eye, the dots are almost impossible to see. I had actually worked with this printer for more than two years before I got a good look at them.

They were revealed because I finally saw them against a dark surface.

One day, when the printer was acting up, we opened the front panels and slid out the black belt. This shiny, electrostatically-charged belt holds the specks of toner in place just before they get melted onto the paper in the fuser.


In the margins of the page, and on a light-colored solid area on the page, I could plainly see a little block of 47 tiny dots repeated dozens of times.

Here is a close up of the yellow dots of toner on the black belt.

I've read that these dots are added as part of a secret arrangement between the United States Secret Service and the individual printer manufacturers, including Xerox.


Here is a close up of the yellow dots against a green background. The yellow dots are printed across every inch of every page.

A slightly different angle.

Close up on the dots.

What do the dots say? Presumably, the U.S. Secret Service won't tell you.

My first guess was that these dots might conceal an eight digit number - the serial number of the printer, so that it can be traced back to whoever bought it.

The Electronic Freedom Foundation (EFF) has done some clever decoding and determined that the dots do contain the printer's serial number, as well as the time and the date it was printed!

I've been dragging everything I own under the 200x magnification of the Eyeclops Bionic Eye, and this certainly qualifies as a worthy candidate.

Here are pictures of three separate projects from that printer: The blue feather cards, the red beetle cards, and a letter card.

The Eyeclops magnifies the image and sends a video signal to the television. First I tried the feather.

The yellow dots are easiest to see in the lighter areas of the feather, against a white background. The magnification is too powerful to fit the entire yellow dot information block onto the screen.

It is important to note that the yellow marking dots are larger than the dots the printer uses to render the intended image. Even in a 60-70% solid yellow field, this pattern of larger dots would probably be discernable.

A photo of a close up from another part of the feather card.

Obviously, these tracking dots are a big problem if you are planning on printing fake money or passports, and they might not be a big deal if you are just printing marketing brochures or wedding invitations.

Here is a closeup of the letter card. Although the letter printing was black only, colored dots were still printed (this may be because some color printing was done on the same sheet of paper.

The problem with these dots is that there aren't any laws which specify what they can be used for. We enjoy the freedom of the press guaranteed by the First Amendment, but the existence of these dots makes it somewhat less palatable to print anything that might be found to be controversial or volatile.

Here are some brochures you might not want to print if you can't print them anonymously:

  • Guide to Impeaching the Vice President
  • Quiet Places to meet a Congressman
  • The Surgical Guide to Not Having Babies
  • The Illustrated Guide to Making Babies
  • The Federalist Papers
  • Middle Names of the Presidential Candidates
According to the EFF, similar marking dots are sprayed by printers from Brother, Canon, Dell, Epson, HP, Konica, Kyocera, Lexmark, Ricoh, Toshiba and others.

Electronic Freedom Foundation (EFF): List of printers which do or do not print tracking dots

I've seen a lot of new things thanks to the Eyeclops bionic eye, but I think this was the first thing that I wasn't supposed to see.


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