1. An apparatus comprising: a processing unit configured to: obtain image data of a plurality of digital image frames captured by an image sensor of an assumed eye having an iris and a pupil, wherein a first digital frame is captured by the image sensor while the assumed eye is illuminated from a first direction and a second digital frame is captured by the image sensor while the assumed eye is illuminated from a second direction; and detect a characteristic feature of the iris using the obtained first digital frame and the second image frame.