1. A method for controlling an image processing device wherein the contour of a segment forming part of an image is polygonal-approximated so that it is represented by a row of vertex data and said row of vertex data is processed to recognize the shape of the segment, comprising the steps of: formulating an image processing procedure, to be carried out in a central processing unit in said image processing device, as a program using a programming language incorporating a group of image processing instructions corresponding to several basic processing steps in the flow of processing including a polygonal approximation processing procedure, said programming language having variables whose structure is inherently determined by an image input section of said image processing device and by run-time subroutines of said programming language; and executing said program by using said central processing unit and an image processing section of said image processing device, wherein said image processing instructions comprise an image input instruction having image variables, a segmentation instruction having image variables, a structure analysis instruction having image variables, a polygonal approximation instruction having image variables for the input image, a polygonal pattern matching instruction, and a characteristic value extraction instruction for recognizing a shape of a segment, said image processing device performing the steps of: inputting a composite of images in response to said image input instruction, including obtaining said composite of images from an image detector and storing said composite of images in an image memory through an image input section; storing information regarding segments into a segment table by segmenting images selected from the inputted composite of images in response to said segmentation instruction; obtaining a positional relation among said selected images from segment information from the segment table and selecting an image to be recognized in response to said structure analysis instruction; polygonal-approximating the selected image to be recognized in response to said line-segmentation instruction and obtaining a vertex coordinate row relating thereto and recognizing an orientation and a position of said selected image to be recognized by processing said vertex coordinate row selectively under control of the polygonal pattern matching instruction or the characteristic value extraction instruction, so that said polygonal approximation processing procedure can be made suitable for a particular use by changing the combination of the basic processing steps and by providing branches in dependence on intermediate results according to the different uses.