Unfortunately, the scenario isn’t fictional. Most color laser printers and color copiers are designed to print invisible tracking codes across every single printed page of their output. These codes reveal which machine produced a document and, in some cases, when the document was printed or copied.
In this instructable, we’ll describe three different ways to see the tracking dots your printer produces: with a blue light, with a microscope, or with a scanner. If you don’t have the necessary equipment for a particular step, go on to the next one.
For further information, or to share your findings, please visit us at http://www.eff.org/issues/printers.
Want to help?
Step 1: Print a Page With Text/graphics
As you’re looking for the dots, keep in mind that they’re printed in a regularly repeating pattern across the entire page (not just in the corner of the page), and will be intermixed with other printed data.
Step 2: Blue Light (w/ Unaided Eye) Method
Turn off all the lights, and eliminate as much ambient light as possible. Shine a blue LED light on the blank part of the printed page. As examining a printer page under blue light improves the contrast, the yellow dots should appear black.
If you have good close-range vision, you should then be able to see them easily. They might initially look like small flecks of dirt or dust. If you can’t see the dots this way, check to be sure that your printer is known to produce them, and try asking a friend to have a look.
Step 3: Scanner Method
The dots can be seen easily by enlarging the scanned image, or by performing a color separation in software and examining the blue channel. A wide variety of image-processing software can perform color separations.
Here are two ways of examining the blue channel with free/open source software:
1. In GIMP, go to Layers, then Channels, then Paths. In the channels tab, deselect the Red and Green channels.
2. With ImageMagick, run the following command at a command line (represented here by the $ prompt):
$ convert -channel RG -fx 0 scan.tiff blue.png
This creates a new image blue.png containing only the blue channel.
You can also try converting to greyscale, by mapping the blue channel’s value to intensity:
with ImageMagick, run the following command:
$ convert --fx b scan.tiff grey.png
You can also do this interactively in Python if you have the Python Imagining Library (PIL) installed. From a Python prompt, run
>>> import Image >>> Image.open(scan.tiff).split().show()
to see a greyscale image formed from the blue channel’s intensity.
PIL can also help enhance the contrast. For instance, you can try the following to sharpen the color contrast between the dots and the page:
>>> import Image >>> blue = Image.open(scan.tiff).split() >>> blue.point(lambda x: (256-x)**2).show()
Step 4: Magnifying Glass or Microscope Method
Step 5: Now What?
- Learn more. Visit us online at http://www.eff.org/issues/printers/.
- Show your friends. Despite repeated media interest — and limited acknowledgments by printer companies — the existence of yellow tracking dots and similar digital fingerprints is still a complete surprise to almost everyone. Some people even express skepticism that these tracking techniques really exist. You can help spread the word just by showing your friends that the dots are there.
- Send EFF your print samples EFF is continuing to collect sample output from color laser printers to help our research. You can download a PDF file from our web site, print test sheets on your color laser printer, and send them to us in the mail.
- Contact manufacturers via the Seeing Yellow site. It’s outrageous that manufacturers make secret deals to compromise our privacy. What’s worse, some printer companies have assumed that people who object must be counterfeiters. The Seeing Yellow project from the MIT Media Lab is helping individuals get in touch with printer companies to express privacy concerns and ask the companies to turn off the tracking and stop building surveillance features into communication technology. You can find contact information for your printer manufacturer — or manufacturers of devices you’re considering purchasing. http://www.seeingyellow.com