1. An image processing apparatus, comprising: image reading means for reading an image of a document that includes an original image portion and an additional image portion overlapping each other; image processing means for forming a processing image based on the image read by the image reading means; and extracting means for extracting the additional image portion from the image read by the image reading means, wherein the additional image portion represents a forming condition for forming the processing image by the image processing means, the image processing means forms the processing image in accordance with the forming condition based on the additional image portion extracted by the extracting means, and the processing image formed by the image processing means corresponds to the original image portion obtained by removing the additional image portion extracted by the extracting means from the image of a document read by the image reading means.