Patent ID: 7903270

Claim:
An image processing apparatus comprising: a first unit for calculating a degree of similarity between image information of a first region on a scanned sheet and previously registered information of the first region on said sheet as image information; and a second unit for calculating a degree of similarity between image information of a second region, wherein the second region is another region on the scanned sheet containing the first region, and previously registered information of the second region on the sheet as image information, wherein the image processing apparatus, if the calculated degree of similarity by the first unit is greater than a first threshold and less than a second threshold having a greater value than the first threshold, calculates said degree of similarity by the second unit; if the calculated degree of similarity by the first unit is less than or equal to the first threshold, controls to terminate the process for calculating said degree of similarity to display an indication that the scanned sheet is not an original paper; and if the calculated degree of similarity by the first unit is greater than or equal to the second threshold, controls to terminate the process for calculating said degree of similarity to display an indication that the scanned sheet is an original paper, wherein the first unit and the second unit ignore dark regions in the image information of the scanned sheet and dark regions in the previously registered information of said sheet as image information when the degree of similarity is calculated, and wherein if f1(x,y) represents the image information of a first region on a scanned sheet and α1(x,y) represents the dark region in the image information of the first region, and f2(x,y) represents previously registered information of the first region on said sheet as image information and α2(x,y) represents the dark region in the previously registered information of the first region, then, the degree of similarity calculated by the first unit is indicated as ∑ α ⁢ ⁢ 1 ⁢ ( x , y ) ⁢ α ⁢ ⁢ 2 ⁢ ( x , y ) ⁢ { f ⁢ ⁢ 1 ⁢ ( x , y ) - f ⁢ ⁢ 2 ⁢ ( x , y ) } 2 ∑ α ⁢ ⁢ 1 ⁢ ( x , y ) ⁢ α ⁢ ⁢ 2 ⁢ ( x , y ) .