IMAGE GENERATION METHOD, IMAGE GENERATION SYSTEM, AND NON-TRANSITORY COMPUTER-READABLE STORAGE MEDIUM STORING PROGRAM

A processing device generates a marker image to use as a reference for correcting a shape of a projection image projected on a projection surface from a projector, takes a taken image of the projection surface using the imaging device from an imaging position different from an observation position from which the projection surface is observed, generates a parameter for reducing a distortion of the projection image based on the marker image included in the taken image, displays an area image representing a range wherein projection can be performed on the projection surface on the display device, disposes a video content at an indicating position in the area image with an input to the input device, generates an original image including the video content, and corrects the original image thereby generating an input image for input to a projector configured to project the projection image.