Quiet Encoding: How Your Laser Printer Manufacturer Has Embedded An ID Code On Every Page You Print

Every page printed with a laser printer contains unique markings that may be traced back directly to the exact laser printing unit that was used to create the page. This discovery has spawned interesting ideas for applications, especially in forensics, but also raises concerns about the implications for people's privacy.

The "Banding" effect: not visible in the first, it is very noticeable in the bottom image

Technological Fingerprints From Every Color Laser Printer
In a PC World news article, titled Government Uses Color Laser Printer Technology to Track Documents, Jason Tuohey, who is a reporter for Medill News Services, wrote this week:

"According to experts, several printer companies quietly encode the serial number and the manufacturing code of their color laser printers and color copiers on every document those machines produce. Governments, including the United States, already use the hidden markings to track counterfeiters."

Tuohey writes that with the help of a looking glass and an LED flashlight, which emits blue light, you will see that the printer's serial number is coded as numerous tiny little yellow dots scattered evenly across the page, thus leaving an identifiable signature behind.

Here some further issues to consider:

Forgery and Counterfeit
Quoting a US Secret Service spokeswoman Tuohey continues, "The only time any information is gained from these documents is purely in [the case of] a criminal act". What the lady refers to is that forging official documents like passports and counterfeiting bank notes has become a worldwide profitable business that is hard to control without the help offered by printer manufacturers.

Train Ticket Fraud
In the Netherlands the Railway Police is investigating a possibly large-scale fraud with counterfeit train tickets. The described marking technology supposedly allows the police to trace a laser printer back to the retailer who sold the printer and perhaps from there to the individual who purchased the printer.

Impossible To Circumvent
Forget about trying to disable the technology. Quoting Peter Crean from Xerox, Tuohey writes:

"Crean describes the device as a chip located "way in the machine, right near the laser" that embeds the dots when the document "is about 20 billionths of a second" from printing. "Standard mischief won't get you around it," Crean adds"

Embedded Web Server
Another journalist, Barry Fox of New Scientist magazine, discovered that a similar technology was patented by Hewlett Packard a couple of years ago. He mentions the technique in his article titled We know what you are printing and also describes why modern laser printers ship with an embedded web server:

"Four types of laser printer now on sale in Britain are leaving the factory with an "embedded Web server" inside it effectively giving each printer a URL. The toner cartridge contains a microchip which monitors the toner supply and tells the embedded Web server how much is left. The main aim is to let IT managers use a central browser to login to various printers and check how many need a new toner cartridge."

Printer Forensic Research
Even without the help of deliberate fingerprinting techniques, researchers from Purdue University, Lafayette Indiana, have succeeded to match laser printed pages to the originating printer, merely by investigating the marks any printer leaves on a printed page. Analogue to an actual human fingerprint, the patterns caused by the rotating drum in the toner cartridge appear to be unique to each printer. In technical jargon this laser-printer fingerprint effect is called banding. Technically, banding is generally defined as the "horizontal imperfections in the print quality of documents".

One of the researchers at Purdue University, Emile Venere, has done an excellent job, not only at describing the cause of "banding" but also at testing and finding out how this visual artifact can be manipulated to positive ends. (Look again at the image at the top of this page: the top one is a manipulated image that shows how banding can be made invisible.)

More details about banding and its "technologically advanced" uses in this article titled Printer forensics to aid homeland security, tracing counterfeiters. The article also mentions that the researchers at Purdue are collaborating with US Secret Service officials.

The Need To Be Well-Informed
Now the question arises where all this is taking us. I can hardly blame forensic researchers that they are seeking help from scientists and printer manufacturers to catch forgers and counterfeiters. And they probably don't have the capacity nor reason to investigate whatever interesting pages are coming out of my printer. Of course I could also just stick with my good old black-and-white laser printer or my inkjet in an attempt to protect my privacy. But the issue is exactly here: printer manufacturers should at least pay me the respect to inform me about the hidden technological tour de force they impose upon printer consumers like me.

I'm having visions that before too long my state-of-the-art refrigerator will ping the Department of Health Care, or even worse, my health insurance company, and discretely inform them that my habitual food consumption doesn't match the latest government recommendations.

Scary idea and probably only showing the tip of the iceberg, especially if you add the fact that apparently printer manufacturers have been embedding these techniques since 1995 already.

What do you think?