Xerox Machines Change Documents After Scanning

PHOTO: Xerox scan error
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The next time you scan a document, you may need to check whether all the numbers add up. A glitch recently discovered in Xerox's WorkCentre machines has been changing numbers on scanned documents, possibly for several years without the company's noticing.

The glitch was discovered by David Kriesel, a computer science researcher at the University of Bonn in Germany. He initially thought he was the butt of a practical joke when an architecture firm claimed that numbers on blueprints that Kriesel scanned earlier were altered. "I thought they were kidding," he told ABC News. "But I tried it myself without and the numbers changed [after being scanned]."

The glitch doesn't affect documents scanned using the machine's default settings. However, if the user changes the WorkCentre's compression settings, this type of error can occur. Francis Tse, a principal engineer at Xerox, wrote on the company's blog to address the glitch.

"The problem stems from a combination of compression level and resolution setting," Tse wrote. "The Xerox design utilizes the recognized industry standard JBIG2 compressor which creates extremely small file sizes with good image quality, but with inherent tradeoffs under low resolution and quality settings."

Kriesel said that it's more than just a resolution problem, but that JBIG2 actually changes the numbers in the scanned image. He explained that the document is segmented into discrete sections and that the WorkCentre machine compares each section to a library of stored patches. "You only need to save a representative patch," he said. "If a section looks like the number 8, then it gets replaced by the representative 8 patch."

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Unfortunately, replacing each section with representative patches can result in errors. Kriesel documented some of these changes in his blog. Some models of the Workcentre machines consistently make the same substitution errors, for example replacing the same 6s with the same 8s. Others models make arbitrary number substitutions that are not consistent each time the machine scans a document.

Bill McKee, a spokesperson for Xerox, told ABC News that the company is developing a patch that will disable the highest compression mode and eliminate the possibility for character substitution. In addition, McKee said that the WorkCentre's printing, copying, and fax functions are unaffected. Tse wrote on the company's blog that the machines now provide a warning message when users scan at lower resolutions, saying that substitution errors may occur.

Kriesel informed Xerox tech support of the problem soon after he discovered it. However, almost none of the people he spoke with knew about the issue. He has spoken with both Tse and Rick Dastin, the company's vice president about the severity of this error. "This problem is dangerous," said Kriesel. "If something is compressed with JBIG2 and I claim it's incorrect, you can't prove me wrong."

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