An image processing apparatus is disclosed. The image processing apparatus stores image data read by a document reading section and image data received from an external device. An image data synthesizing unit synthesizes first image data read by the document reading section and second image data read by the document reading section or received from the external device. An image correcting unit generates image distinctive data of the first and second image data. A synthesized image distinctive data generating unit synthesizes the image distinctive data of the first and second image data by referring to an LUT (lookup table) selected by a synthesized image distinctive generating rule selecting unit. A predetermined process is applied the synthesized image data based on the synthesized image distinctive data.