An example information processing system performs a process based on a captured image captured by an image-capturing device. The information processing system obtains information regarding brightness of each pixel based on the captured image. The information processing device calculates position information of the captured image, the position information representing deviation obtained with the brightness of each pixel being used as a weight. The position information is calculated for a predetermined area of the captured image. The information processing device performs a predetermined information process based on the position information.