An image processing method for extracting a thread-like structure (GW) represented on the background in a digital noisy original image (IM1), comprising steps of acquisition (1) of the original image data; extraction (2) of elementary pixel strings (A1,A2,.) associated in string sets (SA,SB,SC), each of a same threadlike structure, forming a string set image (IM2); operation (4) of a First Phase (Intra-Set Phase) automatically yielding one Best String (A,B,C) per string set (INSI); and/or operation (5) of a Second Phase (Extra-Set Phase) automatically yielding one Final Best String (FBS) by linking Best Strings or elementary strings when the Second Phase is directly carried out (EXSI), for representing the threadlike structure (GW). Application: Medical Imaging; X-ray apparatus with image processing means and display means.