The general field of the invention is that of systems for detecting the posture of a moving object. The system may include a fixed electro-optical device of known orientation comprising an emission source, an image sensor and image analysis means, and an optical assembly comprising an optical retroreflector arranged on the moving object. The optical retroreflector of the system is an optical sphere of variable index comprising a transparent hemisphere and a reflecting hemisphere. It comprises a meshing comprising at least three opaque wires, of small thickness and known geometrical arrangement. The image of the retroreflector lit by the source forms a reflection on the image sensor, said reflection comprising at least the two images of the shadow of one of the three wires. The image analysis means detect the orientation of the leak line given by said images, said orientation being representative of one of the parameters of the posture of the moving object.