Another day, another letter voicing privacy concern lands on the desk of Amazon boss Jeff Bezos.

A day after two senators demanded answers on how Alexa listens and records conversations, a group of 19 Amazon investors have written to Bezos asking the world's richest man to stop selling the Rekognition facial recognition system to governments.

Sent by the American Civil Liberties Union, the letter was joined by an online petition and a second letter signed by almost 70 US organizations voicing similar concerns. Shareholders and those who signed the petition are concerned about how the Rekognition tool could be used to automate widespread surveillance, and the identification and tracking of anyone.

Rekognition is already used by at least one law enforcement agency, the Washington County Sheriff Office in Oregon, according to a testimonial page of customers on Amazon's own website.

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The ACLU said: "Today's actions mark mounting pressure on Amazon to end its practice of selling its dragnet surveillance system, Rekognition, to local enforcement following the release of emails and other documents obtained by the ACLU revealing how the company has been pushing its face recognition product."

In their letter, the Amazon shareholders said Rekognition "may not only pose a privacy threat to customers and other stakeholders across the country, but may also raise substantial risks for our company, negatively impacting our company's stock valuation and increasing financial risk for shareholders."

Kade Crockford, director of the ACLU of Massachusetts' Technology for Liberty program, said: "We cannot blindly stumble into an artificial intelligence-powered surveillance state overseen by corporations interested in expanding their profit margins and police departments committed to exercising limitless power. True public safety - especially for people of color, Muslims, immigrants, and dissidents - requires that we stop the spread of face surveillance before it's too late."

What is Amazon Rekognition?

Amazon describes the "continually-learning" Rekognition as an AI-powered system which "makes it easy to add image and video analysis to your applications. You just provide an image or video to the Rekognition API [application programming interface], and the service can identify the objects, people, text, scenes, and activities, as well as detect any inappropriate content. Amazon Rekognition also provides highly accurate facial analysis and facial recognition on images and video that you provide."

Amazon goes on to say the system can be used for "user verification, people counting, and public safety use cases."

Many potential uses for Rekognition are harmless, such as the ability to overlay player names on the broadcast of a sports match in post-game analysis. In the UK, broadcaster Sky News recently used Rekognition to identify guests as they arrived at the wedding of Meghan Markle and Prince Harry.

But its use by government agencies is a concern for the ACLU. The union's letter to Bezos says: "People should be free to walk down the street without being watched by the government. Facial recognition in American communities threatens this freedom. In overpoliced communities it could effectively eliminate it...With Rekognition, Amazon delivers these dangerous surveillance powers directly to the government."

Amazon is yet to comment on this week's Rekognition news, but said in a May statement: "Our quality of life would be much worse today if we outlawed new technology because some people could choose to abuse the technology."

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