In the aftermath of the September 11 attacks on New York, there was considerable demand for the US to upgrade its airport security mechanisms. Who could forget seeing the images of the hijackers walking through airport security? Their grim faces looked determined, yet profoundly unworried about the possibility of being caught. The public rightly asked how this could have happened. The men were known to the FBI. Any security officer looking at the camera should have been told to watch for their faces and stopped them! The reality of the situation is that the men could not have been caught simply by the cameras at security. There are too many people passing through the checkpoint systems each day to stop anything other than a handful of well known terrorists. One tempting solution is to implement a biometric security system to automate the check. The most tempting solution is likely facial recognition technology, a kind of biometric measurement system already out there in the market.
Facial recognition works by measuring the heights and shapes of many different parts of the human face. Take enough points of measurement and you’ll have a fairly uniquely identifier for an individual. The more points you take – the more accurate the measurement. Think of it like a fingerprint for your face. Facial recognition has the advantage of not requiring the examined individual to touch anything. All he needs to do is look at the camera for a moment to be checked. The computer takes facial measurements from a camera and compares them against a database of known individuals. If there is a match – or a close match at least – the person can be stopped for further questioning. The solution sounds tempting, doesn’t it? We already use it on a human level, don’t we? A driver’s license is kind of like a facial recognition system at the human level. No one looks the same everyday (think "bad hair day", acne, makeup) but somehow we can tell who somebody is by looking at a picture of them and comparing. That kind of heuristic is what makes it so easy for lay folk to understand what facial recognition is. That’s a key to its potential success as a biometric security feature for the next generation of security systems. The last question to ask is how sensitive facial recognition technology is. What if a guy walks in wearing a stocking over his head? What if he has a (fake) eye patch? What about sun glasses? What if he grows a beard? How about if he wearing a mask? The answer for airport security is that the guards will probably stop the guy with the stocking or the mask on. But the other attacks are a bit more troubling. Recent research by folks at University of Pennsylvania have shown that facial recognition systems are robust against a lot of simple attacks, but some of the more tricky one (beards, eye patch) really will confound the system. Now we can’t stop everyone who has a beard at security (although the razor companies might give us a hoot if we did), so we will still need to leave humans in the loop for the time being for some of the curve-balls people can throw at these systems.
