Confused Xerox copiers rewrite scanned documents, expert finds

Scans made by some Xerox copiers are changing numbers on documents, a German computer scientist has discovered.

David Kriesel found that scans he made of construction plans had altered room dimensions.

Other users have replicated the problem, which has been blamed on faults with compression software used in a setting offered by the models.

The company has not yet issued a fix for the problem, but it told the BBC it was preparing a statement.

Mr Kriesel said he worried that numbers could be altered on invoices and other important documents.

He questioned whether incorrect figures could leave a company liable to legal action.

Niri Shan, a partner at London-based law firm Taylor Wessing, told the BBC it could raise interesting legal implications.

"The person who provided the figures would be liable. Then the question would be, could they turn round [to the manufacturer] and say, 'Hold on a minute, this is your fault'?

"Often in commercial contracts, the manufacturer may have limitations of liability on consequential loss."

In his tests, Mr Kriesel found that often the number "6" would be turned into an "8", and vice versa, with other numbers being affected too.

One room on his reproduced plans had its dimensions shrunk from 21.11m to 14.13m.

He said the anomaly is caused by Jbig2, an image compression standard.

Image compression is typically used to make file sizes smaller.

Jbig2 would substitute figures it thought were the same, meaning similar numbers were being wrongly swapped.

Mr Kriesel said the two models affected were the Xerox Workcentre 7535 and 7556.

However, since posting details of the fault online, several other users have come forward with problems on other machines.

This story was updated on 7 August 2013 to reflect the fact that Xerox said the problem only affects scans made under a certain setting by its machines.