1. An image processing apparatus for generating a copy forgery inhibited pattern image, comprising: a generation unit configured to generate a copy forgery inhibited pattern image by determining a pixel value for each pixel of the copy forgery inhibited pattern image based on a bigger dot pattern, a smaller dot pattern and a region designation image, wherein the bigger dot pattern is a pattern comprising a predetermined number of pixels in which a plurality of pixels having a value of 1 are concentrated to form a bigger dot, wherein the smaller dot pattern is a pattern comprising a predetermined number of pixels in which a plurality of pixels having a value of 1 are separated from each other by pixels having a value of 0, to form scattered smaller dots, wherein the copy forgery inhibited pattern image comprises a plurality of regions, each region comprising the same predetermined number of pixels as the bigger dot pattern, and wherein the generation unit prevents the copy forgery inhibited pattern image from having groups of adjacent dots at a boundary between a bigger dot pattern and a smaller dot pattern, even if a boundary between a bigger dot area and a smaller dot area in the region designation image does not coincide with an edge of a bigger dot pattern, by using a pixel value of the region designation image at a pixel position corresponding to one predetermined pixel position in each respective region of the copy forgery inhibited pattern image to determine, for every pixel in the respective region, whether to adopt a pixel value of a corresponding pixel position in the bigger dot pattern or a pixel value of a corresponding pixel position in the smaller dot pattern.