Facial recognition software attaches numerical values to different facial features, creating a unique "faceprint," which can then be checked against a database of existing faceprints. As with fingerprints, a match is assumed when a certain threshold of shared values in the two faceprints has been reached.
Facial recognition software has been proposed as a potentially useful way to prevent terrorists from making their way unrecognized through airports. However, there are a few major challenges, among them setting up a reference system against which terrorists could be recognized. As security technologist Bruce Schneier, points out, "If the biometric is face recognition, you can take good pictures of new employees when they are hired and enter them into the system. Terrorists are unlikely to pose for photo shoots."
The 9/11 attacks reduced public resistance to biometric techniques such as facial recognition software in public places, even those where terrorists are no more likely to show up than anyone else, such as football stadiums. Philip E. Agre, a professor in the Department of Information Studies at the University of California, has argued strenuously against facial recognition software in public places. Agre suggests that not only is the potential for abuse of such systems "astronomical," but also that they are highly unlikely to be effective.