1. A method comprising: accessing a first captured image of a first displayed image produced at a first point in time, and a user; accessing a second captured image of a second displayed image produced at a second point in time, and the user; accessing first information indicating motion associated with one or more objects in the first and second displayed images; determining second information indicating both motion of the user and the motion associated with the one or more objects in the first and second displayed images; and determining the motion of the user by comparing the first information and the second information.