1. An image processing apparatus which extracts, from image data, drawing-photograph pixels forming a drawing or a photograph, the image processing apparatus comprising: a pixel value replacement unit configured to replace original pixel values of image data with plural representative pixel values based on the original pixel values; a candidate region extraction unit configured to extract plural candidate regions, wherein each of the plural candidate regions is formed by a rectangular shape, and includes plural pixels being adjacent to each other and each of the plural pixels has the same representative pixel value; a feature value acquisition unit configured to acquire a feature value indicating certainty that symbol pixels forming symbols are contained in each of the plural candidate regions; a feature value determination unit configured to determine that each of the plural candidate regions in which the symbols are contained based on the feature value does not include the drawing-photograph pixels, and an integration unit configured to integrate other candidate regions that are determined to have the drawing-photograph pixels and that have an overlapping part.