Thursday, January 27, 2011

Will Facebook's choice of social authentication (face CAPTCHAs) lead to huge gains in facial recognition software?

We've actually talked about this sort of thing considerably within my research group, so it's hardly a new idea, but it's still interesting because I hadn't heard of a large scale implementation of this before: Nevermind CAPTCHA, Facebook Asks If You Know Your Friends.

They're calling it "social authentication" where rather than reading obfuscated text as in a normal CAPTCHA, you're asked to identify friends.

"Instead of showing you a traditional captcha on Facebook, one of the ways we may help verify your identity is through social authentication," writes Rice. "We will show you a few pictures of your friends and ask you to name the person in those photos. Hackers halfway across the world might know your password, but they don't know who your friends are."

Of course, that's not true at all. For many people with public profiles, flickr accounts, etc. it's pretty easy for a hacker to identify your friends. (Even easier if your would-be hacker is a jilted lover or angry sibling, but presumably those folk could also pass a regular CAPTCHA.) The key here isn't that this social authentication isn't hackable, though, it's that the hack has to be more carefully crafted to your account, and may well require a human to do the facial recognition necessary, thus slowing down the attack and doing exactly what CAPTCHAs were intended to do.

I'm curious to see how well it works in practice, though. CAPTCHAs in their current "mangled text" form relied on assumptions about the ineffectiveness computer text recognition... assumptions that have been rapidly broken as determined attackers and researchers have improved our text recognition algorithms. (Nowadays, many captchas can be bypassed with a higher than 90% success rate. Here's a link to one such paper but a websearch will turn up many others.)

So the interesting question to me is "Will Facebook's choice of Face CAPTCHAs lead to huge gains in facial recognition software?" -- we're well overdue for gains in that area, actually, given that law enforcement is hoping to use facial recognition to stop crime and even terrorism, but the technology is so poor right now that if they used it now they'd likely be arresting a lot of innocent folk. Facebook will lead to some great cases: What about when your friends are in costumes? Wearing different makeup? Different lighting? Different poses? Different hair?

Beyond the usual halloween costumes, my facebook friends include theatre geeks, haunted house aficionados, members of the 501st legion of Star Wars costumers and folk involved with things like the Society for Creative Anachronism. Will my friends' and acquaintances' penchant for elabourate costumes mean that I'm more secure? Or will it mean that I'll have more trouble identifying them in photos unless I've seen their standard costumes before?

Mostly I'm torn between excitement at new gains in image processing and a vague sense of unease when I contemplate the potential applications of better facial recognition software.


Timmyson said...

I have many "friends" on Facebook who I haven't seen or even communicated with in years. As do many of the friends with whom I got into friend-count competitions. I doubt my ability to accurately spell a random friend's name with better than 60-70% accuracy.

Gail Carmichael said...

This is definitely interesting. I'm also not sure whether to be flattered or worried that you want to offer me for hacking pleasure. ;)