The study presents automatic identification of lungs area and rib borders detection in digital chest radiograph. There are used several segmentation methods, region labeling and region convex hull construction algorithm in lungs identification. Their final shape is derived from lungs identification algorithm, which uses machine learning. Ribs' borders detection is based on Canny's edge detection algorithm. Image of chest radiograph processed by Canny's algorithm is used as entry point to the ribs' border detection. Then, there are presented successive stages of borders detection for a sample rib. There is also described a method of gathering new patterns of ribs' borders.