An image processing apparatus includes a scanner configured to read an image formed on a sheet along a reading direction and generate image data thereof, and a processor. The processor is configured to select a first region of the generated image data into which a first image indicating the reading direction is to be combined, set a pixel value of the first image in accordance with a pixel value of a pixel around the first region, and combine the first image having the determined pixel value into the first region of the image data and output the combined image data.