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Watermarks Help I.D, Printer, Copier Documents


We learned this from research conducted by the Electronic Frontier Foundation: Documents printed on a Xerox DocuColor laser printer have an embedded code, dots invisible to the naked eye that identify each individual printer. Each printer has its own code. These tracking codes could help track counterfeit bills, or they could be used to trace the origin of documents. Professor Edward Delp of Purdue University has worked on a similar system.

And, Professor Delp, first of all, how common is it today that, say, a high-end printer that somebody might have at the office has this kind of coding that could trace a document to it?

Professor EDWARD DELP (Purdue University): Oh, I think they're--it depends upon the manufacturer and things like that. But I think many of these high-end, particularly color laser printers and copiers have some form of technology to either prevent certain things from being copied or printed or put tracking information in the document.

SIEGEL: And is this all about counterfeiting currency?

Prof. DELP: Yeah, it's mainly driven from counterfeiting because counterfeiters are beginning to use these types of devices to be able to essentially print money.

SIEGEL: How do you do it? The thing that the--what the Electronic Frontier Foundation found in the documents printed on the Xerox DocuColor laser printer were sort of a series of yellow dots that you would have to look at with a magnifying lens or under blue light. And inside the dots, there'd be various codes. Are you working along similar lines?

Prof. DELP: No, ours is a little bit different. We're actually looking at modifying how the printer actually puts marks on the paper. We're exploiting certain abnormalities or defects that every printer has when it actually makes or prints a document--forms or print a document. And we'll be able to--and in one case, be able to detect those modifications so we can essentially trace the document back to the printer or, in other cases, be able to, in a sense, maybe add some more subtle variations of these modifications so we can also then trace the document back to the printer.

SIEGEL: So you're picking up from where the old typewriter identification left off.

Prof. DELP: Yes. In a sense, it's similar to that, although it exploits some of the newer, much more advanced technologies, both in how printers print documents and how you can do analysis to be able to detect those defects.

SIEGEL: The Electronic Frontier Foundation raised some civil liberties concerns about this, about how, you know, the leaflet that's been copied on the copier could be linked to the protester perhaps. A concern of yours at all or not?

Prof. DELP: Oh, no, it's very much a concern of our research. We talk about this every time we have a project meeting, and we have project meetings once a week. We worry about issues of civil liberties. I mean, you know, this research, in a sense, in sort of a sinister-use mode, can--you know, we could make a printer that could essentially spy on you. And so it's very much a concern of ours. And, you know, we are developing the technology and we're also looking at methods for sort of mitigating it--you know, `How would you turn it off?' We're even looking, in our research, at methods of how you would attack the technology.

SIEGEL: I guess we all think so much of the computer that the idea that the printer is the identifiable culprit is quite interesting.

Prof. DELP: Yeah. Yeah, it is. I mean, it's another--I mean, you know, it's a--we're looking at a whole set of problems very similar to this at Purdue. We're even looking at very similar things with digital cameras. In other words, I give you the image--you give me the image, and I tell you which camera took the picture.

SIEGEL: You can do that?

Prof. DELP: Yeah.

SIEGEL: And the printer you can do that, too, now?

Prof. DELP: And we can do it with scanners, also.

SIEGEL: It's all identifiable.

Prof. DELP: Yes.

SIEGEL: And are the forensics people up to speed on all this?

Prof. DELP: Well, I mean, it's a new form of forensics. We sort of call it the forensics of things or sensor forensics. And, you know, there's a very large research community looking at sensor forensics right now.

SIEGEL: So anyone who thinks that they can take a digital picture or print out on a laser printer and think that they can be guaranteed anonymity is wrong.

Prof. DELP: Yes. Anyone who thinks they can do that is wrong.

SIEGEL: Professor Delp, thank you very much for talking with us today.

Prof. DELP: Oh, sure. No problem. Take care.

SIEGEL: That's Edward Delp, professor of electrical and computer engineering at Purdue University. He spoke to us from West Lafayette, Indiana.

MELISSA BLOCK (Host): You're listening to ALL THINGS CONSIDERED from NPR News. Transcript provided by NPR, Copyright NPR.

Robert Siegel
Prior to his retirement, Robert Siegel was the senior host of NPR's award-winning evening newsmagazine All Things Considered. With 40 years of experience working in radio news, Siegel hosted the country's most-listened-to, afternoon-drive-time news radio program and reported on stories and happenings all over the globe, and reported from a variety of locations across Europe, the Middle East, North Africa, and Asia. He signed off in his final broadcast of All Things Considered on January 5, 2018.