This morning, Facebook announced that it's going to start scanning all the photos uploaded to the social network looking for your face, unless you opt out - or unless you are a European or Canadian, where privacy law actually limits what Facebook can do with people's faces. The purpose of the scanning, according to Facebook, is to alert you if someone has publicly uploaded a photo of you that you don't know about, especially if they are trying to impersonate you.
Behind the message about protecting your identity, though is a larger truth about Facebook's ability to reach into your personal business: The announcement means that Facebook's face-recognition technology is now so powerful that it can recognise you in any photo, anywhere, even if it has no other reason to expect to find your face in that photo.
It's easy to identify your face if Facebook is only looking for you among the photos your friends have uploaded. It's harder if the possible pool is more than a billion people, a.k.a. Facebook's entire user base. That Facebook thinks it can do the latter means Facebook believes its faceprints are really good now.
And that, in turn, means Facebook has a new powerful tool for mapping who knows who on the social network. By looking at photos from an event, for example, and identifying the faces, Facebook could know everybody who was there and know they might be connected. That would be a boon for Facebook's People You May Know tool, allowing it to suggest as friends people whose faces appeared in the background of photos it identified you in, or vice versa.
That surveillance power would be more than a little creepy - connecting you, for example, to people wandering around behind you as you pose in front of the Eiffel Tower or to people caught in the background when you drunkenly take a selfie at a bar. Given that potential creepiness, and our longstanding interest in how People You May Know actually works, a Facebook spokesperson pre-emptively sent us a note about the facial recognition tool.
"Wanted to give you a heads up about an announcement we made this morning.
"I can also confirm that we do not use this technology in People You May Know."
If that should change, I am sure Facebook will let us know.
This story was produced by Gizmodo Media Group's Special Projects Desk.