1. An image generation system comprising: an image information acquisition section that acquires image information from an image sensor; a grasp motion determination section that determines whether or not a player has made a grasp motion with one hand that is a right hand or a left hand based on the image information; a grasp-linked motion determination section that determines whether or not the player has made a grasp-linked motion with the other hand based on the image information when the grasp motion determination section has determined that the player has made the grasp motion with the one hand, the grasp-linked motion being a motion that follows the grasp motion; and an image generation section that generates an image based on the determination results of the grasp motion and the grasp-linked motion.