As for civilian use, iris scans are reliable enough that they have been used in some European airports for a couple of years now to automate passport control for frequent fliers who are willing to register a grayscale image of the front of their eyes with authorities.* Several British airports are now going one step further and testing facial recognition software that allows travelers to skip the immigration lines and process themselves into the country.
As facial recognition software gets better and better, concerns over privacy for ordinary citizens have mounted. The best results occur when the software can compare high-definition images taken in standardized settings—not a frequent locale for a shadowy terrorist.
But millions of people already have such images of themselves on file in their driver's licenses. In 2009, the FBI used facial recognition software to nab a suspect in a double -homicide who they believed had fled from California to North Carolina. The authorities compared a 1991 booking photo of the suspect against the 30 million photos that the North Carolina Department of Motor Vehicles had on file. Twenty-eight photos came up as possible matches. An FBI analyst then whittled the number down to just one man, who was later arrested and positively identified as the fugitive.
Editor's Note (5/3/11): This sentence was changed after publication to reflect the correct portion of the eye registered in images. Also, "retina" was changed to "iris" throughout for accuracy.