An image processing apparatus combines a background image, handwritten image, and a standard image. A reference image acquired by increasing the luminance value of the background image and the standard image is printed on a recording sheet. A recording sheet is read after being filled in, and a region whose luminance value is lower than a predetermined threshold value and a region indicated by standard image mask data are extracted. The extracted regions are combined with the background image and printed. In particular, the standard image mask data indicates a region in the standard image which is easily affected by a background color of a paper, so that color adjustment is performed on the region in the extracted image which is indicated by the mask data. As a result, the region in the standard image is prevented from being affected by the background color of the recording sheet in the combined result, and the images can be combined and printed according to the original color of the standard image.