Hollywood filmmakers have a strange fascination for this form of biometry. This fascination probably stems from the fact that people understand much less about the eye than they do of hands and fingerprints. Besides, the technology looks pretty cool too. Now, though both these forms of biometry deal with the eye, iris and retinal scans follow two completely different methods of identification.
In iris scans, the iris is photographed using a fairly conventional CCD camera, and the resultant image is compared to the template image that’s stored in the database for iris characteristics such as filaments, crypts, striations and freckles.
Of both the eye scanning biometrics, iris scanning is less intrusive and the apparatus employed is much simpler as well. In fact, iris comparisons can even be done from two photographs-provided the iris is a minimum of 70 pixels, to capture the details of iris patterns.
Lets take the case of Sharbat Gula, National Geographic’s famous Afghan girl. The magazine’s ace photographer, Steve McCurry, first shot a picture of her in 1984 when she was just 12 years old. Later in 2002, when National Geographic began looking for their most famous cover girl, McCurry was skeptical that the woman they had tracked was really the one. Years of war and suffering had taken their toll, completely changing the way she looked. The most conclusive evidence turned out to be the iris comparisons made between two photographs taken 18 years apart. The woman they met was the girl they were looking for!
Moving on to retinal scanning, in this form of biometry, the capillaries at the back of the eye are analyzed. The scanning device uses a low-intensity light sourcemostly infrared. A proper scan requires that the subject focus on a given point while a video camera captures the retinal pattern. This pattern is then converted into data that can be analyzed for matching purposes. Retinal scanning, though a fairly accurate form of biometry, does create problems for those using spectacles.
In the past, iris and retinal scanning was only used for restricting access to certain high-security departments in the US government and military-probably why filmmakers are so enamored by it.