Printer Fingerprints:

PCWorld reports:

Next time you make a printout from your color laser printer, shine an LED flashlight beam on it and examine it closely with a magnifying glass. You might be able to see the small, scattered yellow dots printed there that could be used to trace the document back to you.

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.

Peter Crean, a senior research fellow at Xerox, says his company's laser printers, copiers and multifunction workstations, such as its WorkCentre Pro series, put the "serial number of each machine coded in little yellow dots" in every printout. The millimeter-sized dots appear about every inch on a page, nestled within the printed words and margins. . . .

The dots' minuscule size, covering less than one-thousandth of the page, along with their color combination of yellow on white, makes them invisible to the naked eye, Crean says. One way to determine if your color laser is applying this tracking process is to shine a blue LED light--say, from a keychain laser flashlight--on your page and use a magnifier. . . .

Oh, and here's a rather ambiguous item:

Lorelei Pagano, a counterfeiting specialist with the U.S. Secret Service, stresses that the government uses the embedded serial numbers only when alerted to a forgery. "The only time any information is gained from these documents is purely in [the case of] a criminal act," she says.

Well, which is it -- only when alerted to a forgery, or only when investigating any criminal act?

Thanks to reader Richard Gould-Saltman for the pointer.

Craig Oren (mail):
Gene, I'm not positive about this, but I believe that, aside from protecting the President, the Secret Service's only other responsibility is to investigate forgeries. (The Secret Service was long part of the Department of the Treasury, of all places,and for all I know it still is.) Question: would the Secret Service use the serial numbers to investigate a threat to the President? Answer: isn't that the silliest question ever asked?
7.27.2005 6:43pm
Craig Oren (mail):
Actually, the Secret Service became part of the Department of Homeland Security in 2002, and its investigate responsibilities have been expanded to credit card fraud. But I think my point remains.
7.27.2005 6:47pm
They've been doing this for years. I remember reading a clever technique for revealing the pattern by scanning and then applying some heavy duty photoshopping, but can't find it online now.

Slightly related, and (to a geek like me) funny: most currencies use a pattern of circles to aid machine detection of currency. Last time I had my driver's license renewed, I worked out how far they have you stand from the camera, and the size of the end image, and had a t-shirt printed with the pattern at the correct size, repeating around the neck line (yes, the shirt looks really rather strange). Turns out that the photo resolution isn't high enough (at least in CA) to accurately reflect the pattern, so one can still color-copy my license, but I thought it was worth a try.
7.27.2005 7:55pm
Doug Sundseth (mail):
The Secret Service also investigates computer crime. For an example of their history in such investigations, see (for example). I note EFF says that the case referenced here was the proximate cause for its own creation.
7.27.2005 7:56pm
TomHynes (mail):
Any volunteers to hack into the firmware on the laser printer and change the serial number to something arbitrary and obscene?
7.27.2005 8:02pm
Eugene Volokh (www):
Even if the Secret Service uses this information only to investigate forgery, I wonder whether other government agencies would use it for other purposes. Perhaps they should -- it's just that the article is far from clear on this.
7.27.2005 8:30pm
Cold Warrior:

They've been doing this for years.

That's right. And investigation of documents for possible criminal forgery charges (think counterfeiting) is not the only reason.

I prosecuted a deportation case in which the applicant introduced evidence that he was a member of a banned group in another country. The letter looked good to the nonspecialist (like me): nice letterhead, signed by the proper person, etc. Ordinary forensic document examiners found no indicia of forgery or fraud: the paper type was from the purported country of origin, there were no alterations to the document, the document appeared to have been created several years ago as alleged by the applicant.

But not so fast ... it was referred to Secret Service. They were able to reveal the embedded high-quality color printer codes.

The document was created at a Kinko's outside Seattle.
7.27.2005 11:12pm
Cold Warrior:
A clarification re: my comment above.

Introduction of a fake document (along with foundational testimony under oath about who produced the document and how it was obtained) is also perjury. So being "alerted to a forgery" is often the equivalent of "investigating a criminal act."
7.27.2005 11:16pm
Dan1 (mail):
When will I be able to get a subpoena for this info in a private lawsuit?
7.27.2005 11:17pm
arbitraryaardvark (mail) (www):
The article leaves it unclear whether the printer companies do this for the fun of it, or because the government tells them to. If the latter, it's my opinion that they are engaging in a violation of the right to anonymous speech per Talley v california. Related issue: a guy was busted in my town because he put out mixtape cd's that didn't have a label saying what the content of the disk was - this also would violate the right to anonymous speech. There are legitimate concerns about counterfitting and copyright violations, but this is too broad an infringement on freedom of the press. We have the first amendment because of peter zenger, who was prosecuted for anonymous printing. This topic is also being discussed at slashdot today.
7.28.2005 2:00am
Cold Warrior:

The article leaves it unclear whether the printer companies do this for the fun of it, or because the government tells them to.

I don't know the history, but I am pretty certain it's neither of the above. Rather, the government asks them to.

Of course, you could see this as an offer they can't refuse, since the unspoken assumption is that the government could always seek to ban (or severely restrict) the sale of high quality color printers unless the manufacturers convince the government that these tracking features will make counterfeiting sufficiently difficult.

If the latter, it's my opinion that they are engaging in a violation of the right to anonymous speech per Talley v california.

Well, no, provided they are only using it for the stated purposes -- investigating credible reports of a forgery and/or a criminal act. If the Government suddenly starting using the features to track the origin of an anonymous, non-criminal political manifesto, I think my answer could be different. But the line is not exactly bright here: take, for example, "crime-facilitating speech" of the sort Prof. Volokh has addressed.
7.28.2005 2:33am
The technique described is an application of steganography, a cryptogrphic means of hiding a message in plain sight.

Years ago I designed a set of algorythms to implement steganographic encoding of information into scanned images, with the intent of attaching traceability information to the images. After some work, our firm decided to consult some lawyer-folk who drew into question the notion of deliberately tampering with data that is intended as archival material.

My questions as they relate to the stego-printer: at what point would artifacts introduced into printed material render it unusable for material submitted as evidence? Are there relevant traceability standards for printers and scanners, and the work product that passes thtough them?
7.28.2005 2:53am
"Well, which is it -- only when alerted to a forgery, or only when investigating any criminal act?"

Does it matter?
7.28.2005 11:24am