Eye spy: all the ID you'll ever need. Credit: © J. Daugman

They may be the mirror of your soul, but your eyes are also a built-in passport. Everyone's intricate iris pattern is unique, an analysis of more than 2 million eye images now reveals, offering mathematical support for security systems - soon to be tested in London's Heathrow airport - that could provide personal identification in the blink of an eye.

Using an algorithm that converts the intricate pattern of furrows and ridges in the coloured ring of the human eye into a 2000-bit barcode, mathematicians John Daugman and Cathryn Downing of the University of Cambridge, UK, have carried out the most extensive ever comparison of iris pictures from public tests of iris-recognition systems1.

Iris recognition, they conclude, is almost error-proof. The likelihood of getting a matching code when comparing two images is as low as 1 in 7 billion, Daugman estimates. "That's where the power of iris recognition comes from," he says.

Fooling the system is almost impossible, Daugman's research reveals. Even genetically identical twins and the left and right eyes of the same person have iris barcodes as different as unrelated eyes.

Biometric identification systems, such as fingerprints, face, voice, hand shape and iris recognition, are more secure and convenient than existing authentication systems, explains Tony Mansfield of the National Physical Laboratory in Teddington, UK.

Body of data: a biometric barcode. Credit: © J. Daugman

Unlike personal identification numbers for bank accounts and passwords for computers, biometric identifications are part of your body. "You don't need to remember anything," he says. Such systems are being tested for banks, computer log-ins and access to high-security areas.

Mansfield and colleagues recently found iris recognition based on Daugman's algorithms to be the most accurate of all the marketed biometric systems. It made no false matches in more than 2 million comparisons2.

But the system of choice depends on the application, points out Mansfield. Besides accuracy, time is also a factor. "If you've got a big queue of people you don't want it to take half an hour," he says.

From October this year, frequent fliers at Heathrow airport may be bypassing passport control, breezing through immigration with a quick eye photo. Making an iris image takes less than two seconds, says Catherine Kaliniak of EyeTicket Corporation, providers of the technology for the six-month evaluation.

Although iris colour is determined by genetics, many features of iris patterns - like those of fingerprints - seem to be produced by random, 'epigenetic' events during embryo development. Eye specialists proposed in the 1930s that these patterns might be used for identification.