A startup boasted on Tuesday that it had created a technology to recognize people's faces from photos posted online, causing a stir among some privacy advocates who worry about the implications of automated matching.

The tool--from Swedish startup Polar Rose--converts two-dimensional images into three-dimensional profiles to compensate for colors and shadows and then applies a facial recognition algorithm to the result. The company is relying on its users to enter the names of known people into the database, turning a neat technological trick into valuable data.

The ability to recognize people in any photo--albeit only if the face is 100 pixels or more wide--has set off alarms for people concerned about privacy. The U.K. non-profit group Cyber-Rights & Cyber-Liberties spoke out against the technology in a New Scientist article published on Tuesday, and users have commented on the privacy concerns as well.

"In theory, you're creating your own user-generated photo ID database for the world to see," stated one user's comment posted to Flickr. "Is that ethically (or) even remotely correct?"

Since 9-11, the U.S. government and industry has had an increasing interest in using biometrics and facial recognition to recognize terrorist suspects. However, the technology has not lived up to early promises as an easy way to pick a face out of a crowd. More limited uses, such as recognizing a person standing in a line, hold a greater chance of success, experts familiar with the technology have told SecurityFocus.

Polar Rose believes its technology will change people's perceptions about photos on the Web in much the same way that Google, Yahoo! and Alta Vista changed people's perceptions about text documents. Google hacking, for example, has resulted in Social Security numbers, and other privacy information inadvertently published to the Web, being exposed.

"We’ll end up finding photos that the (publisher) never really thought of as being public," Polar Rose stated in a blog entry published on Wednesday. "The trick, however, is not to turn off the technology, just like Altavista or any of the subsequent search engines weren’t shut down or otherwise censored. The challenge is to facilitate a way to make sure that photos that shouldn’t be in our database, aren’t. This can be by restricting access or by telling us not to pick them up."

Polar Rose's technology is currently in beta and seeking public testers.

UPDATE: The article was updated with comments from and a link to a blog entry on privacy posted on the Polar Rose site late Wednesday.