A recent post on Slashdot:

“According to a report from German computer scientist D. Kriesel, some Xerox WorkCentre copiers and scanners may alter numbers that appear in scanned documents. Having analyzed the output of two such devices, the Xerox WorkCentre 7535 and 7556, Kriesel found that âoepatches of the pixel data are randomly replaced in a very subtle and dangerous wayâ: in particular, some numbers appearing in a document may be replaced by other numbers when it is scanned.”

I see what they did there.