1. An image processing apparatus, comprising: a scanning unit configured to scan at least one of two surfaces of a printed material on both of which information is printed, and to obtain a density image representing intensity distribution of diffuse reflection light from the scanned surface and a gloss image representing intensity distribution of specular reflection light from the scanned surface; a mask image generating unit configured to generate a mask image for the scanned surface based on the obtained gloss image; and a show-through removing unit configured to perform mask processing on the density image using the generated mask image to generate a show-through-removed image that does not include show-through information for the scanned surface.