Rock fractures mapping is very important in many rock engineering applications. To successfully applying automatic image processing techniques for the problem of automatic rock fracture detection and description, the hardest task is the automatic detection of fractures robustly in images. A so-called valley-edge detection algorithm ("valley" or ("ridge") means here finding locally dark (or bright) line-like features) is one-pass line detection algorithm (without thresholding step). The developed fracture detection algorithm is the robust for ridge edge detection and fracture tracing, but for the rough surface with thick cracks or fractures, using multi-scale technology can alleviate producing noise fractures. The algorithm has been tested for detecting fractures. Results indicate that this approach is useful in this domain of images.