Between the iris and the cornea of the human eye there are complex band- and comb-like connective tissue structures. These structures are unique to every person. They even differ in identical twins. In addition, they do not change much in a healthy eye over a lifetime. An image of the iris taken from the outside with a conventional camera (e.g. a CCDcamera) shows these structures, thus making it a suitable feature for unambiguous identification.

However, the structures are difficult to recognise in visible light in people with dark eyes. To overcome this challenge, biometric iris recognition systems light up the iris from a distance of about one metre with light in the near infrared range that is almost invisible to the eye. This light penetrates the pigment of the human eye (melanin) better than visible light.

This means that all people with health eyes can have an image taken of their iris structures without being blinded. Using mathematical methods developed specifically for this purpose, a unique data set is created from the images taken, which serves as what is known as a "template" for biometric recognition.

A general overview of iris recognition is available here (PDF).