Identifier Code and Colour Printers

By Patricia Jordan



Most colour printers leave an identifier code on each piece of paper that is printed. Several years ago, the United States Secret Service asked manufacturers of colour printers and photocopiers to include technology in their products that would allow them to track the source of print material.

The technology behind the identifier code is clever and consists of a series of yellow tracking dots that are invisible to the eye under normal light. They are printed across the entire page, including blank portions of the page. These yellow tracking dots can be viewed with a blue LED light in a darkened room, under magnification or by using a high-resolution flatbed scanner. Zooming in will reveal the yellow dots when they are present. To enhance the dots more clearly, you can use software like Adobe Photoshop to show the blue channel of the image where the dots are more visible. The dots are printed in a specific pattern that allows authorities to identify the individual who printed a particular piece of paper based on the printer. The dots can identify the serial number of the printer and often includes the time and date the page was printed.

The Electronic Frontier Foundation (EFF) has deciphered many marking schemes used by manufacturers. EFF has published a list of colour printer and photocopier manufacturers that use this technology on their website at www.eff.org. Monochrome laser printers and inkjets do not appear to leave identifier code.



Seeing Yellow is a resource site created by the MIT Computer Culture Group that contains information about yellow tracking dot technology.