I briefly worked with a company that made a facial recognition app for Google Glass (http://www.nametag.ws http://www.nametag.ws). Google officially banned us

I briefly worked with a company that made a facial recognition app for Google Glass (http://www.nametag.ws http://www.nametag.ws). Google officially banned us but you could still sideload it. The two major issues were assembling the database of faces (we used mainly LinkedIn photos but you really need multiple photos per person in different light/angles to train it well) and hardware performance (we had to do processing server side but even the basic part running on Glass killed the battery and made it run very hot). The hardware is Glass is basically an underclocked original Moto Droid (the one that launched Android 2.0), and is extremely underpowered for doing local face recognition on a large corpus of faces. I imagine a Glass-like device created a few years from now could be much more viable for this sort of thing. As for the database of people, there are companies that will sell you that (FullContact, Spokeo, Pipl, AllThePeople.net, etc) although the photo quality can still be an issue.