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Xerox Copiers Randomly Alter Numbers In Copied Documents

xeroxA preview of how our society eventually crumbles – subtle sabotage by algorithms in everyday machines? The FontFeed on a mind-boggling discovery:

Last Wednesday German computer scientist David Kriesel had a bizarre discovery. After scanning a construction plan on a Xerox Workcentre and printing it, he noticed the plan suddenly contained incorrect numbers. The Xerox Workcentre somehow changed the numbers whilst scanning.

On his website Kriesel analyses what causes the problem in Xerox Workcentre 7535 and 7556 machines – a compression algorithm randomly replaces patches of pixel data in an almost unnoticeable way.

Apparently Xerox machines use JBIG2, an algorithm that creates a dictionary of image patches it considers similar. As long as the error generated by these patches is not too high, the machine reuses them instead of using the original image data.

Why is this issue so crucial? First of all, these are widespread machines, commonly used in service centres and copy shops, and Xerox seemed to be unaware of the issue until David Kriesel notified them last Wednesday.

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