Skip to content

OPLIN 4cast #347: Photocopier gotcha

Posted in 4cast

xerox copierWe have a confession to make. We used to chuckle at people using the library photocopier who carefully compare their fresh copy to their original document. That’s crazy behavior! Except now it turns out that it’s not so crazy after all. Three weeks ago, a German researcher looked closely at one of his photocopies and discovered that it did not match the original. Even more astounding, Xerox (the company that made his photocopier) admitted that it is possible for a photocopier to mistakenly change a document. Really?! If you can’t trust your photocopier, what can you trust?

  • Xerox scanners/photocopiers randomly alter numbers in scanned documents (David Kriesel) “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.”
  • Update on scanning issue: software patches to come (Real Business at Xerox/Ken Ericson) “We continue to work tirelessly and diligently to develop a software patch to address the problem. We’ll pass along information about the timing of the patch as soon as we have it. We want to reiterate, we believe the issue deals with ‘stress documents,’ which include documents with small fonts, those scanned multiple times and hard to read.”
  • When copiers aren’t copying as they should… (From Page2Pixel/Isaiah Beard) “Of course, the expectation is that the PDF will exactly match the original paper document. There’s just one problem: an absolute, exact copy would mean generating large, uncompressed images, resulting in huge PDF files that would be difficult to pass around in e-mail attachments, and cost a lot of money to store on large hard drives for archival purposes. For many corporate settings, this would be a deal-breaker. So, to keep file sizes down, nearly all of these copy systems (not just Xerox) compress the scanned images, using the industry-standard JBIG2 algorithm.”
  • Security flaw with a difference – the Xerox scanner that makes your house smaller! (Naked Security/Paul Ducklin) “It turns out that the Xerox scanner in question was using a compression scheme called JBIG2, which emerged from the grandly-named Joint Bi-level Image Experts Group. Bi-level images, as the name suggests, have just one bit per pixel, such as the images used in fax machines (if you remember them). And JBIG2 has a clever, yet, with hindsight very reckless, feature: if two ‘swatches’ of the image look like each other, the same data is used for both swatches, so that they effectively become identical.”

Copiers fact:
So far, the copiers primarily affected by this problem seem to be older Xerox WorkCentre machines. See the list posted by Xerox.