Abstract: Specially designed for the fully automated detection of residual oxide stains (residual scale) and classification thereof in metal sheet production lines, with no to stop the line, the invention consists of a framework or box (4) equipped with means for movement (8) over the surface of the metal sheet (2) to be examined, containing a high-resolution CCD camera (1), a high-power lighting unit (6-7) and a diffuse light generator; the video signal of the camera is sent to a PC (3) equipped with software for processing the images obtained, so that the residual oxide stains may be detected and classified. The movement of said box or framework (4) is controlled by a programmable automaton (14), also connected to said PC (3).