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Comment by cosgroveb | Hacker News Reader

The social captcha idea is neat, but sometimes my friends tag each other in pictures that aren't of them (cartoons - or places) sometimes to joke around with each other or get a friend's attention. I can see someone getting locked out of their account for being shown a picture which Facebook thinks has a given friend in it but in reality does not.

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They actually have face-recognition algorithms that only show you pics where the face is clearly visible now.

This is probably also a really clever use of captcha as a way to train their face-recognition algorithm.

They already have the faces annotated via the tagging system. To be really sneaky they could inject faces which have been detected but NOT tagged. However they probably have enough data anyway - enough being the largest facial recognition training data set in the world.

The tagging made by users in their photos and face recognition is different.

When a user has to tag someone they are given standard sized box to drag over the person you want to tag while the face recognition systems selects only the face of the person no matter how big or small it is on the picture.

Pedantic note: face recognition != face detection != face verification.

Quite a few people seem to have thousands of "friends" on their list, most of which they don't actually know personally; they are there because they both play some kind of game (Mafia Wars, Farmville, etc). So the social captcha idea wouldn't work in that case either...

I think another intention of this is making it more difficult for people to keep those fake profiles.

That's what the skip button is for.

How exactly does social captcha slow down someone who has hacked into your friends' accounts and has seen a lot of tags on photos of friends in your friend network?

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