An image processing system includes a projection unit that projects an image onto a projection surface; a photographing unit to take a photograph of an area including the projection surface onto which a first content image is projected by the projection unit so as to obtain a first photographed image; a data volume reducing unit to reduce a data volume of the first photographed image through a predetermined processing so as to obtain a second photographed image after data volume reduction; a correction information calculating unit to calculate, based on the first content image and the second photographed image, correction information for correcting an image to be projected onto the projection surface; a correction unit to correct, based on the correction information, a second content image that is the image to be projected onto the projection surface. The projection unit projects the corrected second content image onto the projection surface.