Printer forensics may give counterfeiters pause

The technique uses two methods. The first analyzes a document to identify qualities that are unique for each printer. The second designs printers to purposely embed individualized characteristics in documents. The technique currently focuses on laser printers but eventually will be expanded to inkjet printers.

Counterfeiters often digitally scan currency and then use color laser and ink-jet printers to produce bogus bills. Forgers use the same methods to make fake passports, driver's licenses, and other documents.

So far, the researchers have been able to successfully identify the model of printers used to create certain documents in 11 out of 12 models tested. They believe they will be able to identify not only which model printer was used, but also specifically which individual printer was used.

Officials also would be able to use the method to determine the authenticity of documents, such as airline-boarding passes and passports. Such information would enable homeland-security investigators to determine the country or region of origin for certain printed documents. This information would be helpful in tracing potential terrorists and their collaborators.

The technique uses specialized software to detect slight variations, or "intrinsic signatures," of printed characters, revealing subtle differences from one printer to another. Even printers that are the same model have slight flaws and variations in their mechanical systems. These variations result in subtly different characters.

The researchers have observed variability from printer to printer within a single model. The reason for the variability is simple economics. Production of printers that all behaved exactly the same way would require a tightening of manufacturing tolerances to a point where the resulting printers were uneconomic. The gears, for example, are plastic. There also is variability from one toner cartridge to another. The researchers are able to determine this intrinsic signature based on knowledge of the physical qualities of the printer mechanisms.