Recently, the pattern matching technique is used in various researches in the research area of image processing. Pattern matching technique employs the degree of similarity between two images, and several methods for calculating the degree of image similarity have been presented. This paper describes a new method calculating degree of image similarity. This technique has applied the preliminary lung nodules detection on digital chest radiographs of 30 cases. The results of performance study showed that sensitivity 93%. These experimental results have demonstrated the effectiveness of this technique.