In computer science there ha been increasing interest in development of matching measures for gray scale images. This problem has lots of applications from pure image matching to image retrieving from an image data base. There are various strategies and approaches to image comparison. In the paper we summarize many of them and give a short overview. Various types of low-level measures are studied and their properties are described. We show that measures based on our idea presented in 'vision geometry-95' is the best choice for the low-level image matching SOme new properties of this measure are explored. Several applications for matching strategy based on the measure are given.