The image processing apparatus is provided with a scanner unit that reads a document and generates image data; an edge vicinity pixel detection unit that detects pixels in the vicinity of the edge of the document based on luminance values of the image data generated by the scanner unit; a histogram creation unit that creates a histogram using the luminance values of pixels in a region of the document within a predetermined distance from the pixels in the vicinity of the edge; and a judgment unit that judges whether or not it is possible to separate a document region from a document-external region based on the created histogram.