1. An anti-collision warning system for marine vehicle comprising: at least one optical sensor covering at least partially the horizon of the marine vehicle, and supplying images; an image processor that searches in real time in each image supplied by the optical sensor for groups of adjacent pixels according to the light intensity of each pixel of the image, that assesses a repeated appearance of each group of pixels in a predetermined number of successive images, that extracts groups constituting persistent objects visible on the surface of the sea, according to their repeated appearances while removing groups constituting non-persistent objects comprising at least one of waves, reflections, and foam, and that determines position and dimension information of at least one of the visible persistent objects; and anti-collision analysis control that periodically calculates the evolution of the position and dimension information of the at least one visible persistent object, and that assesses a risk of the marine vehicle colliding with the visible persistent object according to the evolution of the position and dimension information of the visible persistent object.