17. A computer-readable storage device having instructions stored which, when executed by a computing device, result in operations comprising: generating, a level of security desired, a text challenge, wherein generating the text challenge is based on eliciting distinctive behavior of a user when compared to behavior of other users, the behavior of other users and the highly distinctive behavior of the user being stored in a database of dynamic image features; prompting the user to utter the text challenge; recording an audio and a video of the user as the user utters the text challenge, to yield a recording; and performing user verification using the recording.
19. The computer-readable storage device of claim 17 , wherein the recording of the audio and the video yields a dynamic image feature.