Just tap any detected face and give it a name. The app will memorize the face and recognize it further. For best results, hold the device at arm's length. You may slowly rotate the head (or slowly change your location) for the app to memorize you at multiple views. The app can memorize several persons. If a face is not recognized, tap and name it again.
The SDK is available for mobile developers: www.luxand.com/facesdk