As sciguy says, the arduino cannot do these things by its self, but it can talk to other things... Processing will probably be able to handle face recognition, and it has a serial library that can communicate with the arduino. Even if the microcontroller cannot do the job by its self, it is easy to make it talk to processing which can do it for you. The arduino can also move physical things; how about a door lock that uses face recognition to turn a servo and open a door? That way, only you (or a photo of you, or a look-alike) can get in.