Facebook is taking heat, again, for (possibly) violating users' privacy. This time, the uproar is over a new facial recognition feature called "Tag Suggestions." Here, a brief guide to the controversy:

What are "Tag Suggestions"?
It's a technology that uses facial-recognition software to automatically identify and "tag" the people in photos uploaded to Facebook. The feature was initially rolled out in the U.S. last December, and then to the rest of the world this week, leading to complaints and investigations. The tool is automatically enabled for all users by default.

Is this an invasion of privacy?
European Union regulators have launched a probe to find out. "Tags of people on pictures should only happen based on people's prior consent and it can't be activated by default," says one EU regulator. Rep. Edward J. Markey (D-Mass.) concurs, saying that "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."

How else is Facebook using my face?
There's worry that Facebook is building a massive, "potentially sensitive database" of the facial features of its more than 600 million members. "Facebook users thought they were simply tagging their friends," says Marc Rotenberg, with the Electronic Privacy Information Center. "Turns out Facebook was building an image profile database to automate online identification."

What does Facebook say?
The company maintains that it introduced the new feature in response to user complaints about the tedious process of uploading and tagging friends in every photo. The company notes that the feature only makes tagging suggestions, and can be disabled. A Facebook spokesman says they have received few user complaints, so it seems "people are enjoying the feature and are finding it useful."

Do other tech giants have such technologies?
Google says it has facial recognition capabilities, but has hesitated to employ them, because of privacy concerns. "People could use this stuff in a very, very bad way as well as in a good way," says Google chief Eric Schmidt. Last year, Apple reportedly purchased a facial recognition company named Polar Rose.

Sources: CNET, Wall Street Journal, Bloomberg Businessweek