Photo tagging: Facebook is sorry for NOT notifying its users.

Facebook has apologised for launching its facial recognition technology without giving any prior notice to its users.

This feature, which has been expanded from theUnited States to 'most countries', automatically identifies people in photos without their knowledge.

Its 'Tag Suggestions' feature uses facial recognition technology to speed up the process of labelling friends and acquaintances that appear in photos posted on Facebook. If a user's friend tags his or her photo, the technology will automatically scan the user's face and then try and find matches among all their pictures.

Tagged photos typically appear in the user's photo stream, and his or her friends' streams, depending on the settings.

Although Facebook said that it should have notified members about the global launch, it added that the system introduced with an intention to speed up the process of assigning a name to a picture, known as tagging.

Graham Cluley, senior consultant with security firm Sophos, said that users' annoyance was less about the product's purpose than the manner in which it was made live.

"Once again Facebook seems to be sharing personal information by default. Many people feel distinctly uncomfortable about a site like Facebook learning what they look like and using that information without their permission," the BBC quoted Cluley, as saying.

Cluley also clarified that Tag suggestions would not allow the users to identify strangers from their photographs.