1. An image processing apparatus for processing inputted image data defining a first image that includes a picture image and a portion that is not the picture image, the apparatus comprising: a watermark pattern creating means for creating a watermark pattern; a picture image extractor means for extracting the picture image from the first image shown by inputted image data and creating a second image that is a remaining image obtained by removing the picture image from the first image and including a position where the picture image had been arranged; a superimposing means for executing a processing of superimposing the watermark pattern onto the second image including the position where the picture image had been arranged to thereby define a third image; and a document image creating means for superimposing the extracted picture image over the third image in the position where the picture image had been arranged to thereby create a document image that includes the picture image onto which the watermark pattern is not superimposed and the portion that is not the picture image onto which the watermark pattern is superimposed.