Good point, I was only considering the case where FB uses this technique to verify an existing user's identity using facial recognition (which seems like a "log

Good point, I was only considering the case where FB uses this technique to verify an existing user's identity using facial recognition (which seems like a "logical" use case). I missed the part where they said they might use it for account creation as well (which makes less sense and seems like a pretty baroque, intrusive and ineffective captcha).