Breast cancer is now one of the main causes of death among women throughout the world. The diagnosis and separation of cancerous tumors in mammographic images require precise, experience and time, and he always posed himself as a great challenge for radiologists and physicians. Despite the immense danger that this disease presents, its curability is relatively high if it is treated early; that's why it is necessary to develop a computer-assisted diagnostic system (CAD) to facilitate the early detection of this cancer. In this paper, we have implemented such a system. The developed method proceeds in three steps: pretreatment mammograms to remove the breast area, segmentation based on morphological operators to detect breast masses. Finally, the segmentation of the breast contour based on the method of Marching Square was adopted. Our approach has been tested on the basis of pictures"MIAS" showing its efficiency. In addition, a graphical interface was performed to facilitate the task for radiologists.