A German data protection official called Wednesday for social networking site Facebook to delete biometric profiles of people stored without their explicit consent, saying they breach European privacy rules.

In other words, he wants Facebook to delete users' faces from its databases.

Johannes Caspar, head of the Hamburg office for data protection, said talks with Facebook to bring its business practices in line with German and European Union privacy rules had failed. Caspar said in a statement that he is now re-opening a stalled probe of the Menlo Park, California-based company "in order to find a legally sound solution with regard to the use of biometric data."

Caspar is highly critical of Facebook's photo tagging feature, which asks users to attach the names of people in pictures they have uploaded. Facebook then uses the unique facial characteristics in each picture to automatically identify the same person in other photographs on its site. Users can opt out of the service, but Caspar wants them to have to opt in.

"Facebook will be obliged to delete this data unless it obtains approval by all concerned users," he said, adding that "due to the immense potential of misuses of biometric data the explicit consent is a legal requirement for the collecting and processing of biometric data."

Facebook responded with a statement saying that it believes the photo tagging feature "is fully compliant with EU data protection laws."