Bad news about iris scanners

I don’t know about you, but I look forward to the day when I can stop memorizing passwords and use biometric identification (BI) systems instead. Unfortunately, iris BI may not be the ideal solution. According to Samuel Fenker and Kevin Bowyer of the University of Notre Dame, iris BI systems suffer from a phenomenon called ‘template aging’. That is, the inaccuracies in matching the enrollment (template) scan to subsequent scans mount as time passes.

In the case of iris scans, accuracy begins declining almost immediately and rapidly gets worse. After only one year, the false reject rate (the rate at which the system fails to accept that an iris scan is from the same person) went up by 25-60%. After three years, the false reject rate went up by 150%. 

To be clear, these are increases in percentages rather than actual numbers. In other words, if the false reject rate of pictures taken a month apart was one in a million, then three years later that same person would be rejected by a scanner two and a half times out of every million. If this sounds like nothing to worry about, remember that if iris BI systems became widespread with millions of people using the device, there will be many false rejections every day. 

So what causes template aging? The most obvious source of this problem is that a person’s physical attributes have shifted in some way. Contrary to popular opinion, irises do change as people age. However, Bowyer points out that other causes, such as deteriorating imaging equipment or even posture and environment (which might influence how dilated a pupil is) can also attribute to template aging. It's difficult to reconcile the short time frames at which template aging is observed with any of these processes though. Do people's eyes change that rapidly? Do they choose progressively odd positions in front of the scanner as time passes? It's hard to say what exactly is going on. In any case, it's important to be aware of the problem.

The authors believe that there will continue to be a place for iris BI systems, which is good news for companies that are already using it. Perhaps people will have to redo their template scans every year or so. On the other hand, we may discover what’s causing template aging and find a way to compensate for it.