Introduction: Yellow Dots of Mystery: Is Your Printer Spying on You?

Picture of Yellow Dots of Mystery: Is Your Printer Spying on You?

Imagine that every time you print a document, it automatically includes a secret code that could be used to identify the printer -- and, potentially, the person who used it. Sounds like something from a spy movie, right?

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

Want to help? Download test sheets at

Step 1: Print a Page With Text/graphics

Picture of Print a Page With Text/graphics

Print out a page from a color laser printer. The page should use color and have some text or graphics on it. You can find a list of printers that we know print tracking dots at our website.

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

Picture of Blue Light (w/ Unaided Eye) Method

You'll need a blue light for this method. EFF has blue LED lights available, or you can get a blue LED flashlight or any other strong blue light from any other source. An ordinary battery-powered blue LED will work.

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

Picture of Scanner Method

Scan your printed page on a color flatbed scanner at 600 dpi; this makes the dots visible in the scanned image. Modifying the scanner isn't necessary, since it already has a blue light.

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  >>>[2].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 =[2]  >>> blue.point(lambda x: (256-x)**2).show()

Step 4: Magnifying Glass or Microscope Method

Picture of Magnifying Glass or Microscope Method

Place the printed page under a microscope or look at it through a magnifying glass (ideally with a magnification of 10x or more). Even under normal ambient light, the dots are easy to see. We tried two USB computer microscopes (DigitalBlue and Dino-Lite), but any kind of microscope should work.

Step 5: Now What?

Picture of Now What?

Now that you've seen the dots, what can you do?

  • Learn more. Visit us online at
  • 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.
  • Join EFF to support our work on privacy, anonymity, and free speech issues at the intersection of law and technology.

Special thanks to the California Consumer Protection Foundation for funding the project.


AdamK212 (author)2017-06-08

Data outdated.

to see in Gimp, use from an image menu: Windows → Dockable Dialogs → Channels; then deselect red and green.
A better way however is to

Install this script into Gimp

Using these details

Then close Gimp to reboot it and open it to load the new script.

Then scan a color image of something printed out (make sure image has 3 colors to trigger the metadots) at 600DPI (change scan settings of printer, they may not show at the default 300DPI)

load the scan into Gimp, Next select

Filters. "Filters->Politics" and click ''Show yellow tracking dots''

image will apply filter and show metadots.

shadowman2 (author)2009-01-05

What about B/W laser printers.

charlieb000 (author)shadowman22016-01-28

I saw on a CSI-like program they said printers put a unique code on the sheet, the prop that they used (from a B&W printer) had a tiny line nearer to a corner of the sheet. i looked for such a line on my prints but never found it... so maybe they do, maybe they dont, either that or the B&W printer has a high DPI so that the dots over the sheet are too small, or maybe the dots are now encoded into the way the printer renders shades of grey/colour (called dithering) - which might be present on printers you have previously thought were OK.

shadowman2 (author)charlieb0002016-01-29

Geez man, thanks for the reply, but my above comment is 7 years old, I even forgot what instructables was.

spitfireap (author)shadowman22017-06-06

You know that these comment posts also help other readers looking for info. A reply to an 8 year old post may help someone else, it's not just for you.

SeanP45 (author)2016-01-27

So, for simple text, wouldn't printing with a yellow background obscure the code to the point that it couldn't be detected?

alex_the_creator (author)2015-06-03

It's the illuminati, I told them, they never listened. I also don't trust toasters, they probably put crazy tracking sh*t in them too.

karakoramcharcoal (author)2015-05-13


devicemodder (author)2014-12-27

what's with all the bots here? their accounts advertise insurance and cruise websites. they are the ones with single word comments and comment the same stuff on other 'ibles.

Colonel Hogan (author)2014-11-04

this is like the NSA spying on our phone conversations

motherprune (author)2014-06-14

Thats sweet

cobbledbeard (author)2014-06-13

his is wrong in so many ways and quite disturbing as well come to think of it...

mousepaper (author)2014-06-12

Its fabulous :)

Christopherhenson88 (author)2014-06-11

Its nice

gorgeddamp (author)2014-06-09

Thats astounding

illrings (author)2014-05-26

Thats cold

airbugger (author)2014-05-22


williamsjavellana (author)2014-05-19

Its extraordinary

headlymph (author)2014-05-08


tealrink (author)2014-05-08


grousebandit (author)2014-05-05

Thats magnificent...

harechubby (author)2014-04-28


jiffymanager (author)2014-04-25


calmlunch (author)2014-04-20


spewlocks (author)2014-04-19


clapfilk (author)2014-04-07


NumerologyAnswers (author)2014-04-03


spongeraffle (author)2014-04-02

Its nice

workexaminer (author)2014-03-28

Thats hip

bearblue (author)2014-02-25


bearblue (author)2014-02-25


gazumpglue (author)2014-02-02

Very weird and strange.

Mariska Botha (author)2013-09-04

Very weird and strange.

BunnyRoger (author)2013-09-03

Scary facts.

Amanda Culbert (author)2013-09-02

This is wrong in so many ways and quite disturbing as well come to think of it...

MAApleton (author)2013-08-29

I find this just a tiny bit silly, or it it just me?

jillef (author)2013-08-09

What about scanned documents? If a document if scanned from any scanner and then saved as a jpeg and sent as an email where the IP cannot be tracked is there any data that can be found then on those jpegs?

contactscolored (author)2013-03-26

Thank you so much :) You made my day !!

heckstallw (author)2013-03-13

Its usful

mrestivolouise (author)2013-03-13


lujanmarion (author)2013-03-08


rickafost (author)2013-03-07


softenersreviews (author)2013-03-02

sensational and informative

itsme123 (author)2009-07-06

why could not you just print a blank page many times thru different printers ( or print in white something like a period). running it thru top first , then bottom first then thru other printers, it would be hard to tell which printer made which mark making it hard to tell exactly where each mark came from

vov35 (author)itsme1232011-10-20

It's impractical to do so on a regular basis to help prevent being spied upon, but yes, this would cause problems with their system. Congratulations, now the system is only useful for invading our privacy and not preventing fraud. :D

atombomb1945 (author)2008-10-22

"It's outrageous that manufacturers make secret deals to compromise our privacy." What privacy? How many times do you send a letter to some one and you do not want them to know who sent it? This is not any different than your IP address being included in an email or saved at a website.

11010010110 (author)atombomb19452008-10-22

when you print something you expect it to be anonymous unless you intentionally signed it for love letter (do you really want it to be anonymous ?) you probably just print and its anonymous. for some other stuff you may want to use a generic font / shred the text with babelfish / handle the page with gloves. you sure dont want the dots there

Cereleste (author)110100101102008-10-22

The dot's don't identify the person, right? Just the printer. Then this has nothing to do with privacy. The dots will only tell someone that a XXXprinter printed it, not Bob Smith printed it.

11010010110 (author)Cereleste2008-10-22

scenario 1 your boss asked you to print some stuff for him with deadline. deadline passed and you did not do that. boss calls and asks whyits not ready. you tell him you sent and thats the mail service fault (and not yours). you sit to print it and remember to write there the date of 2 days ago (to make the show perfect) boss recieves the mail. he is freaked off how late the docs arrived and shares his rage with a friend. his friend suggests him to check the true date encoded in the dots and decode that using the calculator in the EFF site scenario 2 you are a journalist who uses the computer for his professional stuff as well as his personal stuff. he prints a doccument that he wants to make confidential so that no one can get on him if the document falls in the wrong hands. the document does a month ago his daughter married an he printed the invitation letters on the same printer. one of those letters is enough to link him to the confidential doc via the printer serial number the dots contain information that you did not intend to include in the document you print and you are likely to be unaware of its existence. this is a privacy issue. no need in your name it may be very complicated to find by incident a titled document printed on the same printer - so it does not look that severe. possibilities become huge when dots meet other info that can be esily crossed with them - like where was batch of printers of model X and manufacture date Y sold - probably available from the manufacturer lets wait for the EFF guy to explain more

atombomb1945 (author)110100101102008-10-23

Cereleste, you are correct, the information is just Lexmark - serial number xxxx-xxxxx-xxxxxx and perhaps the date and time. This is not printing out your name, address, and contact information. 11010010110: Both Scenarios are possible, but not really probable. Unless that Boss makes it a policy to look at the dots on each page, then he probably would not even think about it. If someone is using a printer for both "questionable" business practices and personal use, he deserves to be caught. Base line point is this: If you are printing something out that you do not want to be linked to in any way what so ever, make sure you have an older printer that does not support the dot printing.

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