An image processing apparatus carries out a combining process in which a part of an original image is whitened and a target image to be combined is superimposed over the whitened part. The image processing apparatus receives a command to specify a color of an unnecessary region of the stamp image including the target image to be combined which region is not to be superimposed over the original image in the combining process. Then, the image processing apparatus receives a command to define a necessary region of a specified color region of the stamp image which necessary region should not be defined as the unnecessary region, the specified color region being constituted by pixels indicating the color specified by the command. Further, the image processing apparatus carries out the combining process, assuming that the unnecessary region is a region of the stamp image which region is obtained by excluding the necessary region from the specified color region and the target image to be combined is a region other than the unnecessary region in the stamp image.