Original-discrimination system for discriminating special document, and image forming apparatus, image processing apparatus and duplicator using the original-discrimination system

An original discrimination system for determining whether or not an original image is identical to a predetermined reference image, in response to data concerning said original image being input, duplication of said reference image being inadmissible, the determination comprising the steps of:

• a) removing extremely fine lines and isolated dots from the original image,
• b) determining whether in a predetermined area fine lines have been recognized in a number which exceeds a predetermined limit to be allocated to the original image;
• c) interrupting the copying operation when the number equals or exceeds the predetermined limit, and continuing the copying operation when the number falls below the predetermined limit;
• d) determining whether in the predetermined area fine lines are present with equal or unequal distance;
• and
• e) interrupting the copy operation if the fine lines are recognized with unequal distance.