Facebook is coming under fire for a feature that uses facial recognition software to allow members to tag pictures of their friends on the social network.

The "Tag Suggestions" feature made its debut on Facebook in the United States six months ago but has drawn renewed attention this week after the social network began rolling it out to other countries.

Tag Suggestions uses facial recognition software to match newly uploaded photos to photos that have been tagged elsewhere and suggests the name of the friend in the photo for tagging.

Although the feature was launched in the United States in December, it began coming under scrutiny again this week following a blog post by Graham Cluley of the security firm Sophos.

Cluley objected to the enabling of the photo tagging feature without giving users any notice and the fact that it is an opt-in instead of an opt-out process, meaning users were included unless they specifically changed their settings.

"The tagging is still done by your friends, not by Facebook, but rather creepily Facebook is now pushing your friends to go ahead and tag you," Cluley said.

"Facebook does not give you any right to pre-approve tags," he said. "Instead the onus is on you to untag yourself in any photo a friend has tagged you in. After the fact."

"Many people feel distinctly uncomfortable about a site like Facebook learning what they look like, and using that information without their permission," he continued.

"The onus should not be on Facebook users having to 'opt-out' of the facial recognition feature, but instead on users having to 'opt-in,' Cluley said.

A member of the US House of Representatives also objected today to the opt-in nature of the photo tagging feature on Facebook, which has been forced to weather a number of privacy storms over the past few years.

"Requiring users to disable this feature after they've already been included by Facebook is no substitute for an opt-in process," said Representative Edward Markey, a Democrat from Massachusetts.

"If this new feature is as useful as Facebook claims, it should be able to stand on its own, without an automatic sign-up that changes users' privacy settings without their permission," Markey said in a statement.

Facebook, which has more than 600 million members, said today that the feature was intended to make it easier to tag friends in photos but apologised for not sharing more information.