Washington County police are deploying Amazon's facial recognition software Rekognition, and running sketches of suspects through it, The Washington Post reports.

Amazon said the use of sketches doesn't break its rules, but cautioned that police reviewing the results would have to be mindful of the "confidence" rating given by the software.

Experts voiced concern that using sketches would increase error rates, which could lead to false matches and wrongful arrests.

Rekognition's use by law enforcement has already come under fire from civil rights groups, AI experts, and Amazon shareholders.

Visit Business Insider's homepage for more stories.

Police in Washington County are running sketches of suspects through Amazon's facial recognition software, The Washington Post reports.

Deputies are allowed to run black and white sketches through Amazon's software, Rekognition, in the hope that the artist's impression of the suspect finds a match.

It's unclear how effective this method is, but Washington County police told the Post's Drew Harwell that in one test case, using a sketch had identified a man they'd already flagged as a suspect.

AI experts told the Post that using a sketch could increase the likelihood of a false match, a sentiment which was echoed by Privacy International's Frederike Kaltheuner when contacted by Business Insider.

"This adds another layer of complexity that will likely increase error rates," said Kaltheuner, who heads up the organization's programme on corporate exploitation.

Amazon told the Post that using sketches doesn't contravene its rules, but said that it would expect police to "pay close attention to the confidence of any matches produced this way." Confidence is the percentage rating Rekognition gives any match it makes, and Amazon recommends that law enforcement set a threshold of 99% when using the software.

The Post found, however, that deputies weren't even shown this rating when using Rekognition, but were shown five possible matches for each search, irrespective of the system's confidence in its match.

Read more: Artificial intelligence experts from Facebook, Google, and Microsoft called on Amazon not to sell its facial recognition software to police

A previous report from Gizmodo also revealed that police do not necessarily adhere to Amazon guidelines on confidence ratings, with a Washington County police public information officer saying "we do not set nor do we utilize a confidence threshold."

An Amazon spokeswoman told Business Insider in a statement: "WCSO's use of the suspect sketch was an experiment, and not part of the current system that is in use. Regardless, we would expect that the results of any matches would be thoroughly reviewed by humans, that no automated action was taken, and that the reviewers would pay close attention to the confidence of any matches produced this way, in addition to the usual processes surrounding the use of sketches in law enforcement."

The sale of Rekognition to law enforcement has already been sharply criticised by civil rights groups, AI experts, and even Amazon's own shareholders. Investors will vote to ban Amazon from selling the software to government agencies later this month at the firm's annual shareholder meeting.

"Generally speaking, we are quite concerned about the use of facial recognition by police departments — both when it works and when it doesn't. When it works it turns people into walking ID cards, when it doesn't it risks incriminating the innocent who then have to prove that they are not guilty," said Kaltheuner.