Printer tracking dots

Printer tracking dots, also called printer steganography or yellow dots, are tiny marks placed on almost every page printed by color laser printers and photocopiers. These dots act like a secret code that can tell authorities which machine made the printout. They were created by companies like Xerox and Canon in the mid-1980s to help track important documents.

These special dots are usually yellow and very small, so they are hard to see with the naked eye. Even though they look almost invisible, they can be read by scanners or special software. Because every printer or copier has its own unique pattern of dots, experts can often figure out which device was used to print a page.

The existence of these tracking dots became widely known in 2004, surprising many people who thought their printed documents were completely private. Today, these dots are used around the world as a security tool, helping police and other officials solve crimes where knowing who printed a document can be important.

Understanding printer tracking dots helps us realize that many everyday objects, like office equipment, have hidden features that can be used for safety and security. It also shows how technology continues to develop in ways we might not notice in our daily lives.

History

In the 1980s, Xerox made tiny dots on printed pages to show which printer was used. This helped stop people from making fake money. Later, many printer companies did the same.

In 2004, people learned about these dots when Dutch authorities used them to find fake money. Groups like the Electronic Frontier Foundation helped explain how these dots work. They showed that many printers around the world have these tracking dots on their pages.

Technical aspects

Many color laser printers and photocopiers add tiny yellow dots to every page they print. These dots are very small—about one-tenth of a millimetre across—and are spaced about one millimetre apart. They form a pattern that shows information like the printer’s serial number and the date and time the page was printed. This pattern repeats many times across the page, helping to identify the printer.

In 2005, experts from the Chaos Computer Club showed that these printers can store data in their dot patterns. In 2018, researchers at the TU Dresden studied many printer models and found they used different ways to encode this hidden information. Xerox has said that their printers include such markings as a security feature.

Visibility

These tiny dots can be seen by scanning a printed page with a high-resolution scanner. You might also spot them with a magnifying glass in bright light, or under UV-light.

These dots help experts identify copied items, like banknotes, even if they are broken up. In 2011, a DARPA challenge called the "Shredder Challenge" was won by a team that used these dots to rebuild torn documents.

Practical application

Some journalists and security experts have talked about how hidden codes in printed pages can help find out who printed secret documents shared online. This helped discover a person who shared important information without permission.

Protection of privacy and circumvention

Copies or printouts of documents with private information, such as health care records or bank statements, can sometimes be traced back to the printer that made them. Many users don’t know this because the companies that make printers don’t talk about it. In 2005, the Electronic Frontier Foundation created a Python script to help people understand these hidden codes.

In 2018, scientists from TU Dresden made a tool that can read these hidden codes. They shared this tool to help people share important information safely.

Comparable processes

There are other ways to tell which printer was used. These include changing how strong the laser is or using different shades of grey in the text. As of 2006, it was not known if printer makers were using these methods as well.