To provide a method for eliminating illumination irregularity from an image picked up by an overhead projector with an image input function.

The illumination irregularity on the upper surface of a stage is picked up (first image pickup action) and first image data obtained by the first image pickup action is recorded by a microcomputer. The image and the illumination irregularity of a transmissible original on the stage are picked up (second image pickup action) and second image data obtained by the second image pickup action is recorded by the microcomputer. Then, arithmetic operation for deleting the content of the first image data from the second image data is executed by the microcomputer so as to produce corrected image data obtained by eliminating the illumination irregularity. When the corrected image data is recorded, the clear image can be reutilized afterward.