1. An image reading apparatus comprising: an image capturing module for capturing an image of a document; a light source; a movable light reflecting surface having a white color; a driving module for moving the light reflecting surface into a first position at which the light reflecting surface reflects light from the light source and a second position at which the light reflecting surface does not reflect light from the light source; and a control module for controlling the driving module to move the light reflecting surface, wherein the control module determines the second position by moving the light reflecting surface by a predetermined quantity from the first position determined based on an image obtained by the image capturing module.