The image input apparatus comprises the image pickup unit which optically scans a subject and successively acquires partial images of the subject. The relative change detection unit detects an amount of relative change in position or speed of the image pickup unit between a time when a previous partial image was taken and a time when a current partial image is being taken. The an overlapping amount calculating unit calculates an amount of overlap between the previous partial image and the current partial image based upon the amount of relative change in position or speed detected by the relative change detection unit. The image recording determination unit determines whether or not the current partial image is to be recorded based upon the amount of overlap calculated by the overlapping amount calculating unit.