1. An image processing apparatus comprising: a printing unit configured to print an image on a recording sheet; a reading unit configured to read the recording sheet; a conversion unit configured to convert a background image to a reference image which indicates the background image of a higher luminance than the background image; a first print control unit configured to cause the printing unit to print as a region to be written in by a user a first image in which a standard image is superposed on and combined with the reference image acquired by the conversion unit; an extraction unit configured to extract an image of a region having a lower luminance value than a predetermined value from a second image acquired by the reading unit reading the write-in region of the recording sheet written in; an acquisition unit configured to acquire mask data for extracting an image of a region corresponding to the standard image and indicating a color adjustment region of the extracted image; and a second print control unit configured to cause the printing unit to print on the recording sheet an image extracted from the second image using mask data acquired by the acquisition unit and the extraction unit, and superposed on and combined with the background image, in which a pixel of a color adjustment region indicated by the mask data is replaced by a predetermined pixel.