One of the biggest challenges in digital identity is authentication, the process of knowing that the person or system presenting credentials is who they say they are. A driver's license has an authentication system built-in: the picture. Humans are really good at looking at pictures and faces, making a comparison and reaching an accurate conclusion about whether there is a match. For digital ID, the problem is more difficult. At the low end, we use usernames and passwords. More sophisticated systems use retinal scanners and other biometric devices. In this interview with the New Scientist, James L. Wayman of San Jose State University, California, expresses his reservations about biometrics.