In this article I present in which way scanners / copiers of the Xerox WorkCentre Line randomly alter written numbers in pages that are scanned. This is not an OCR problem (as we switched off OCR on purpose), it is a lot worse – patches of the pixel data are randomly replaced in a very subtle and dangerous way: The scanned images look correct at first glance, even though numbers may actually be incorrect.
Think about that for a second. A copier that replaced numbers with no other discernible change in the copy. I don't mean blurring of numbers. I mean substitution. Now think about all of the contracts, medical documents and design plans out there with incorrect information in the copies.
By way of @wilshipley