1. An image processing method of performing an image processing that corresponds to a dot pattern, on an image displayed on a display device, by imaging a medium on which the dot pattern is printed by an optical reading device, wherein a controller as the medium on which dot patterns are printed in a superimposed manner with icon images is used, the dot patterns in which a command code or a coordinate value for the image processing is patterned, the image processing method comprising: selecting a brush to be used for the image processing by sequentially imaging the icon images in the controller by the optical reading device; selecting a drawing color by imaging an icon image in the controller by the optical reading device; and performing a drawing processing on the screen of the display device by scanning with the optical reading device on the controller, the drawing processing corresponding to a trail of scanning.