1. A method comprising: generating, at a level of security, 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 audio and video of the user as the user utters the text challenge, to yield a recording; and performing user verification using the recording.