The Information Commissioner's Office (ICO) has confirmed it has made contact with Facebook about controversial face recognition technology on the site.
The social network came under fire this week for not asking users if they were happy for the Tag Suggestions feature to run.
Instead, Facebook decided to green light the feature, which prompted users to tag friends detected by the technology, run by default. Mark Zuckerburg's firm subsequently apologised, saying it should have been clearer with users.
"As with any new technology, we would expect Facebook to be upfront about how people's personal information is being used," an ICO spokesperson said.
"The privacy issues that this new software might raise are obvious and users should be given as much information as possible to give them the opportunity to make an informed choice about whether they wish to use it. We are speaking to Facebook about the privacy implications of this technology."
The feature was running in the US last year, but has now been expanded to most other countries where Facebook operates.
Graham Cluley, senior technology consultant at Sophos and regular Facebook scrutiniser, was critical of the social network's decision to have the feature run by default.
"Unfortunately, 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," Cluley said in a blog post.
"Most Facebook users still don't know how to set their privacy options safely, finding the whole system confusing. It's even harder though to keep control when Facebook changes the settings without your knowledge."
He said the onus should be on users to opt in rather than have to opt out.
"Yet again, it feels like Facebook is eroding the online privacy of its users by stealth," Cluley added.
Facebook admitted it "should have been more clear with people during the roll-out process when this became available to them."
It said photo-tagging suggestions were only made when new photos were added and only friends were suggested rather than random people.
Many privacy supporters have hit out at Facebook in the past over its practices. The social network has sought to allay privacy concerns with regular updates.
Earlier this year, Facebook started asking users for feedback on the best way to present privacy information and settings to make them simpler.
The company said it wanted to make privacy policies "easy to understand," "visual and interactive" and "relevant" to the questions users wanted answered.
