When estimating color for a marker candidate region that is smaller in size than a DeBayer filter, a sever estimates the color of the marker candidate region using HSV average values that are the average values of the hue H, the saturation S, and the brightness V of the marker candidate region, in consideration of the Bayer array of color filters. Furthermore, the server appropriately corrects the HSV average values and converts the pixel format to convert the HSV average values to RGB (RGB average value values), and sets the RGB average values in all pixels of a marker region.