An image processing system which reads, in pixel units, an image on an original document using a scanner, processes the read image data, and outputs the processed image data. The image processing system includes a system for recognizing a circular image of a specific color. The recognizing system includes a specific color detecting unit for detecting a specific color on an image on an original document; a first image detecting unit for detecting, in the image detected by the specific color detecting unit, images of the specific color at positions spaced from each other by a first distance corresponding to a diameter of a circle on a line extending in a fast scan direction; a second image detecting unit for detecting intersections of the circle having the diameter equal to the first distance and a line separated by a predetermined distance from a center of the circle in a slow scan direction when the specific color images are detected by the first image detecting unit; and a specific color image determining unit for determining that a contour containing the images of the specific color, detected by the three detecting units, is circular on the basis of the detection of a pitch line of a second distance by the second image detecting unit.