Image forming apparatus with security feature which prevents copying of specific types of documents

Claim 1

An image processing device for executing various kinds of image processing, including filtering, magnification change and gamma correction, with input image data, said device comprising: pattern detecting means for determining, pixel data by pixel data, whether or not pixel data constituting the input image data are part of a predetermine inhibition pattern, said pattern detecting means having variable detection accuracy; document deciding means for determining, based on a number of pixel data determined to be part of said predetermined inhibition pattern by said pattern detecting means, whether or not the input image data are representative of an inhibited document inhibited from being copied, said document deciding means having variable decision accuracy; and changing means for changing the detection accuracy of said pattern detecting means and the decision accuracy of said document deciding means; wherein the inhibited document comprises a sheet on which said inhibition pattern is printed or copied over an entire area thereof, wherein said changing means comprises timer means and automatically changes the detection accuracy of said pattern detecting means and the decision accuracy of said document deciding means according to a period of time preset for said timer means, wherein the changing means comprises: a memory for storing different parameters utilized by the pattern detecting means and the document deciding means, wherein the image processing device further comprises a controller which loads different parameters from the memory to the pattern detecting means and the document deciding means, depending on the period of time preset for said timer means.