1. An image processing apparatus configured to create a material in a form of a stack made by a plurality of paper sheets being piled so as to be used in production of a piece of work, the piece of work being made by each of the plurality of paper sheets being cut out along cutting lines formed thereon, the image processing apparatus comprising: a detecting portion configured to detect, based on obtained image data, at least one of color information and density information included in the image data; a correspondence setting portion configured to set correspondence between each of a plurality of section image regions which are made by an image, indicated by the image data, being sectioned based on the information detected by the detecting portion, and either one or both of a color and a density of each of a plurality of paper sheets to be used in creation of the material; a piling order determining portion configured to determine, based on a condition defined in advance, a piling order for a case where paper sheets having either one or both of the colors and the densities whose correspondence with the respective section image regions has been set by the correspondence setting portion are to be used in the material; and a print data generating portion configured to generate, for each paper sheet to be used in the material, print data that includes line images indicating cutting lines in accordance with the piling order defined based on borders of the respective section image regions and determined by the piling order determining portion.