It was ordinary compression, something called JBIG2. It did not mistranscribe, but mark slightly different number or character blocks as same, resulting replaced parts in images.
In other words, its match tolerance is a bit too lax, so it get poisoned by blocks in its own dictionary, thinking it already has the blocks for things it had just scanned.
In other words, its match tolerance is a bit too lax, so it get poisoned by blocks in its own dictionary, thinking it already has the blocks for things it had just scanned.
More details can be found in [0] and [1].
[0]: https://www.theregister.com/2013/08/06/xerox_copier_flaw_mea...
[1]: http://www.dkriesel.com/en/blog/2013/0802_xerox-workcentres_...?