A system and methods for authenticating a user for access to a system input terminal that includes an infrared imager, a user input terminal, and a processing section including a plurality of processing instructions operable to perform image capture for wrist areas of a user in proximity to an input terminal or other structures requiring authentication and comparison to determine access or deny access. An aspect of an embodiment of the invention permits initial and frequent authentication that reduces or eliminates user action to perform such authentication. Also provided are user interfaces, and additional authentication sections operable with the infrared imager. Alternative embodiments of the invention include a mobile embodiment as well as an embodiment-including a sensor positioned with respect to a user in an operational position where the user is performing a task in relation to an input terminal or structure requiring authentication (e.g. a keyboard).