Facebook, which announced in December that it planned to introduce the service in the United States, said on Tuesday that the feature was in fact now available in "most countries" and acknowledged that it should have been "more clear with people during the roll-out process when this became available to them."
The lack of notification about the wider roll-out of the new technology and the fact that Facebook has automatically enabled the technology in users' settings have raised concerns among some privacy advocates, who say it should be up to users to switch it on.
While facial recognition technology is used in other photo products such as Apple Inc's iPhoto and Google Inc's Picasa, Facebook's use of the technology across its social network of more than 500 million users could raise novel privacy issues, according to Marc Rotenberg, president of the privacy-advocacy group Electronic Privacy Information Center.
The Facebook product scans users' newly uploaded photos, comparing the faces in the photos against previously labeled photos to see if it can match any of the people. If a match is found, Facebook alerts the person uploading the photos and invites them to "tag," or identify, the person in the photo.
Facebook said the product helps speed up the process of identifying and labeling people in photos, a popular practice among Facebook users that the company said currently occurs more than 100 million times a day.
Facebook has stressed that the automated photo-tagging suggestions are only made when new photos are added to Facebook, that only friends are suggested and that users can disable the feature in their privacy settings.