[Retric]

This impersonation is only really useful when one person can create multiple fake accounts.

If Facebook can simply run image comparison between the the face used and other accounts while knowing that picture isn’t copied from elsewhere because it includes their onetime key it could prevent duplicate accounts.

In practice I doubt it’s more effective than a new CAPTCHA.

[notahacker]

Not to mention that scammers are relatively unlikely to want to show their face for ID purposes even if it's their only account (whereas ordinary people that want to join a service for posting pictures of themselves on the Internet generally don't mind), especially not when there's a wide world of other scams they can be getting on with that don't involve showing their face.