1. An image processing apparatus, comprising: a scanning mechanism configured to read images; a first memory storing a reference dot pattern indicating an anti-copy background dot pattern; a second memory storing image data; an image accumulating mechanism configured to accumulate image data of an original image which is read by the scanning mechanism into the second memory; a detecting mechanism configured to detect a background dot pattern embedded in a background image included in said image data of said original image accumulated in said second memory; a determining mechanism configured to compare said detected background dot pattern with said reference dot pattern stored in said first memory and to determine whether said detected background dot pattern is substantially identical to said reference dot pattern; and a code assigning mechanism configured to assign an identification code to said image data having said detected background dot pattern and accumulated in said second memory when said detected background dot pattern is determined by said determining mechanism as substantially identical to said reference dot pattern.