1. An image supply device used with an image display device adapted to display an image on a display surface and an operation detection device adapted to detect an indication location in accordance with a position indication operation on the display surface, comprising: a drawing section adapted to generate a superimposition image to be displayed while being superimposed on an original image based on the indication location detected by the operation detection device; a first image generation section adapted to generate a first composite image by superimposing the superimposition image generated by the drawing section on the original image; a second image generation section adapted to generate a second composite image by superimposing an operating image for instructing a process of the superimposition image generated by the drawing section on the first composite image in response to a change in the original image; and an output section adapted to output the second composite image to the image display device.