Computer-generated image data is presented on first and second displays of a binocular headset presuming that a user's left and right eyes are located at first and second positions relative to the first and second displays respectively. At least one updated version of the image data is presented, which is rendered presuming that at least one of the user's left and right eyes is located at a position different from the first and second positions respectively in at least one spatial dimension. In response thereto, a user-generated feedback signal is received expressing either: a quality measure of the updated version of the computer-generated image data relative to computer-generated image data presented previously; or a confirmation command. The steps of presenting the updated version of the computer-generated image data and receiving the user-generated feedback signal are repeated until the confirmation command is received. The first and second positions are defined based on the user-generated feedback signal.