Abstract: Various devices and systems may benefit from convenient authentication. For example, certain mobile devices may benefit from attribute-based continuous user authentication. A method can include determining attributes of an authorized user of a mobile device. The method can also include obtaining an unconstrained image of a current user of the mobile device. The method can further include processing the unconstrained image to determine at least one characteristic of the current user. The method can additionally include making an authorization determination based on a comparison between the attributes and the determined characteristic.