Facebook has sent a cease-and-desist letter to a facial recognition startup after it scraped billions of images from the social media site without permission.

The social media giant told Buzzfeed News it had sent "multiple" letters to Clearview AI about the issue and claimed the startup's actions "violate" its policies.

New York-based startup Clearview AI, which describes itself as operating in "full compliance with the law," develops facial recognition technology for catching criminals used by over 600 US police departments.

Facebook follows Google, YouTube and Twitter in sending a cease-and-desist letter to Clearview AI, with the startup believed to have scaped similar content from those respective platforms.

Clearview's CEO defended the company's actions Wednesday, claiming the firm has a "First Amendment right" to access data in the public domain.

Business Insider has approached Facebook and Clearview AI for comment.

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Facebook has become the latest major tech firm to send a cease-and-desist letter to facial recognition startup Clearview AI over unauthorized photo scraping.

"Scraping people's information violates our policies, which is why we've demanded that Clearview stop accessing or using information from Facebook or Instagram," Facebook's spokesperson told Business Insider.

New York-based startup Clearview AI develops facial recognition technology for catching criminals, and describes itself as operating in "full compliance with the law."

Despite Clearview's relatively low profile, the New York Times estimates that at least 600 police departments across the US use its vast, searchable photo database as part of their law enforcement efforts.

Facebook follows Google, YouTube and Twitter in sending a cease-and-desist letter to Clearview AI, with the startup believed to have scraped similar content from those respective platforms.

On Wednesday, a YouTube spokesperson told Business Insider: "YouTube's Terms of Service explicitly forbid collecting data that can be used to identify a person. Clearview has publicly admitted to doing exactly that, and in response, we sent them a cease-and-desist letter."

A cease-and-desist letter is generally sent to an individual or a company to stop any unauthorized activity and to not restart it.

At heart, the issue seems to hinge on whether there's a real distinction between publicly accessible information and publicly available information. If information is publicly accessible, does that necessarily mean such information is available for others to use as they see fit?

For its part, Clearview has fiercely defended its actions.

In an interview with CBS on Wednesday, Clearview's CEO Hoan Ton-That defended the company's actions, arguing that the firm has a "First Amendment right" to access data in the public domain.

Business Insider has approached Facebook and Clearview AI for comment.