A method for controlling an image processing device wherein the contour of a certain segment of an image, or pattern is polygonal-approximated so that it is represented by a row of vertex data and the row of vertex data is processed to recognize the shape of the segment. This method comprises the steps of describing an image processing procedure as a program by a programming language incorporating a group of image processing instructions, and executing this program by the image processing whereby several different image procedures can be performed for image processing according to different uses. This method also controls the image processing procedure using a program written by a programming language incorporating variables representing the structure inherent in the image data.