Identifying people by scanning the irises of their eyes may not be as reliable as some governments and the public might think. That’s according to new research suggesting that irises, rather than being stable over a lifetime, are susceptible to ageing effects that steadily change their appearance over time.

With iris recognition now being used at border control in countries such as the United Arab Emirates and the United Kingdom, this has huge implications, says Kevin Bowyer, a professor of computer science at the University of Notre Dame in Indiana. At the very least, it could cause delays if people have to be scanned again. At worst, it implies that people might increasingly be able to evade detection when moving between countries.

Bowyer and his colleague Samuel Fenker, also at Notre Dame, used state-of-the-art, commercial iris-matching software to measure differences in the software's performance when comparing more than 20,000 different images of 644 irises, taken between 2008 and 2011. The authors compared the quality of a match between two images of the same iris that were recorded roughly a month apart, to pairs of images taken one, two or three years apart. They found that the rate at which the system failed to match two images of the same iris — known as the false non-match rate — increased by 153% over the three years...