It's hard to identify a person when the set of possible values is "every person on the planet" and not "one of these few persons". They could detect if the uplo

It's hard to identify a person when the set of possible values is "every person on the planet" and not "one of these few persons". They could detect if the uploaded looks like one of the uploader's Facebook friends, I suppose, and that would probably be useful. What would they do if they detect a possible match, though? Ask the person they think is in the photo "is this you, are you ok with John Doe sending this photo to Jane?". That could lead to trouble when the system gives false positives.