SAN FRANCISCO – Facebook on Friday confronted a new obstacle over what to do with one of its most vital assets – pictures.

The company promised European regulators that it would forgo using facial recognition software to automatically identify its users on the Continent, and delete a database that held millions of pictures uploaded in Europe.

The decision could have wide repercussions on how facial recognition technology – a particularly sensitive advance – is used globally as surveillance cameras are increasingly installed in public spaces.

"This is a big deal," said Chris Hoofnagle, a law professor at the University of California, Berkeley, who specializes in online privacy.

"The development of these tools in the private sector directly affects civil liberties," he explained. "The ultimate application is going to be – can we apply these patterns in video surveillance to automatically identify people for security purposes and maybe for marketing purposes as well?"

The agreement comes as Facebook is under pressure from Wall Street to profit from its vast trove of data, including pictures, and also from regulators worldwide over the use of personal information.

The decision in Europe applies to the "tag suggestion," a Facebook feature that deploys a sophisticated facial recognition tool to automatically match pictures with names. When a Facebook user uploads a photo of friends, the "tag suggestion" feature can automatically pull up the names of the individuals in the image.

The facial recognition software was developed by an Israeli company, Face.com, which Facebook acquired for an undisclosed price in June.

The company quietly and temporarily pulled the plug on "tag suggestion" for all Facebook users several months ago. The company said Friday it was to "make improvements to the tool's efficiency" and did not say how soon it would be restored.

However, the company promised European regulators Friday that it would reinstate the feature on the Continent only after getting their approval.

Facebook declined to say under what circumstances the "tag suggestions" would be back online in the United States or elsewhere.

Facebook's promise to the European regulators is part of an investigation into whether the company's data collection practices comply with European privacy rules. It was made with regulators in Ireland, where the company has its European headquarters.

"We will continue to work together to ensure we remain compliant with European data protection law," Facebook said in a statement.

Europe is an important market for the company as it struggles to prove its worth on Wall Street. About 1 in 4 Facebook users logs in from Europe. According to the company's earnings figures, Europe accounts for about a third of its advertising revenue.

Pictures have always been vital to Facebook. Pictures are what drew users to Facebook in its earliest days, and pictures are what continue to keep people coming back.

Facebook users upload 300 million images a day. The company's acquisition of Instagram, the photo-sharing site, eliminated its biggest rival in this area.

Photo tagging is important for Facebook in the sense that it allows the social network to better analyze with whom its users interact in the real world.

In addition to scrutiny from European regulators, Facebook has also come under fire from U.S. consumer protection groups and lawmakers over its use of facial recognition technology. At a hearing on Capitol Hill in July, Sen. Al Franken, D-Minn., described Facebook as the "world's largest privately held database of face prints – without the explicit consent of its users."

On Friday, Franken said in an email statement that he hoped Facebook would offer a way for U.S. users to opt in to its photographic database.

"I believe that we have a fundamental right to privacy, and that means people should have the ability to choose whether or not they'll be enrolled in a commercial facial recognition database," he said. "I encourage Facebook to provide the same privacy protections to its American users as it does its foreign ones."

The Electronic Privacy Information Center, an advocacy group in Washington, filed a complaint with the Federal Trade Commission over Facebook's use of automatic tagging. The complaint is pending. The commission has a consent order with Facebook that subjects the company to audits over its privacy policies for the next 20 years.

Personal data is Facebook's crown jewel, but how to use its trove artfully and profitably is arguably its biggest challenge. Facebook has access to a tremendous amount of information about its 1 billion users, including the photos they upload every day.

Marketers have pushed for greater access to that data, so as to tailor the right message to the right customer. Consumers and lawmakers have resisted, to different degrees in different countries around the world.

"They are pushing the edges of what privacy rules may allow, just as an aggressive driver might with parking rules," said Brian Wieser, an analyst with the Pivotal Research Group, a research firm in New York. "You don't know you've broken a law until someone says you've broken a law."

Several independent application developers are experimenting with how to use facial recognition technology in the real world and have sought to use pictures on Facebook to build products of their own.

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