Privacy regulators are pushing European counterparts to block aspects of a controversial Facebook feature that suggests names for people in newly-uploaded photographs.
The "Tag Suggestions" feature uses facial recognition software to match these images to photos that have been tagged elsewhere and suggests the name of the friend in the photo for tagging on the social network, which has 600 million members worldwide.
Gerard Lommel, director of Luxembourg's data protection agency, said Britain, Germany and Ireland had each also expressed "worries" that the online giant will activate the feature by default, and that even if users have to opt in first, "certain concerns would remain".
The system "leaves people like me -- who are responsible for monitoring the protection of personal data -- pretty much perplexed," he said.
"Where are the limits and how do we apply regulations on data protection so as to be sure that these tools do not work on a universal basis?
"We realise we will have to treat this quickly, in a more detailed way... (However) we will have to find a way to act in a unified way at a European level," he added.
Although the feature was launched in the United States in December, it came under scrutiny again this week as the company indicated its rollout to other countries, and amid objections by bloggers from other big Internet companies.
"Rather creepily Facebook is now pushing your friends to go ahead and tag you," said Graham Cluley of the Internet security firm Sophos.
US lawmaker Edward Markey objected on Wednesday 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 the Massachusetts Democrat.
Facebook said Wednesday that such tagging is "currently done more than 100 million times a day".
Many large media companies are also looking at facial recognition software in a bid to squeeze out more revenue from valuable image banks.
Explore further: What safeguards are in Australia's data retention plans?