[joe_the_user]

I suspect such a system would be harder to create than one would think. Face recognition seems like it's always to going to be too glitchy to guarantee the smooth operation of a "pick it and leave" system. My guess is that the smoothest functioning system would involve rfid's or the equivalent which signal that they were close to a given shopper. Prius and other autos already have doors that unlock only when someone is carrying the key-dongle. And clever ways to hack these system are already here too (amplifiers, for example).