Researchers create tool to anonymize prints with tracking dots

Scientists at the Technical University of Dresden have investigated tracking dots that many printers leave behind on documents. They have developed a tool for analyzing and anonymizing these little yellow dots.

The researchers detailed their findings in a recent paper. They write that tracking dots are still relevant because paper is still widely used and that they have value in determining who or which printer has printed a document.

For example, the small yellow dots that color laser printers leave on documents contain the printer’s serial number and the date it was printed. The scientists examined a total of 106 printer models from 18 different manufacturers. They discovered a total of four ‘point patterns’, one of which has not been discovered before.

Most of the manufacturers surveyed added a pattern to prints, with the exception of Samsung, Tektronix and Brother. While the researchers from the first two manufacturers examined five and four models respectively, only one Brother model was involved. In an older list from the Electronic Frontier Foundation, which is no longer maintained, Brother had tracking dots, but Samsung did not. The different patterns discovered have a varying number of cells in a matrix in which the dots may be present. For example, Pattern 1 uses 512 cells, while Pattern 2 has 414 cells. In this way a number of bits of information can be stored.

The researchers have put the software used to analyze the tracking dots on GitHub. This also makes it possible to anonymize documents. In addition to being able to remove the dots on a scan with imaging software, they state that it is also possible to add more dots to disrupt the pattern and make it unusable. For each pattern found, the researchers tried to develop a mask that anonymizes a document with as few dots as possible.

The discussion surrounding tracking dots came to the fore again about a year ago when The Intercept published a classified document that allegedly reveals such patterns. Around the same time, a woman named Reality Winner was arrested for leaking classified information. She pleaded guilty this week in exchange for a 63-month jail term, The New York Times reported.