1. A method for determining the topography or optical properties of a moving surface of a subject, the method comprising: acquiring a first image of an area of the subject, on an image-formation area, at a first moment in time while aiming a first type of illumination at the area of the subject; acquiring a second image of the area of the subject, on the image-formation area, at a second moment in time while aiming a second type of illumination at the area of the subject, wherein the topography or the optical properties of the moving surface of the subject are determined on the basis of the first and second images; and acquiring images, on the image-formation area, of a reference area located near the area of the subject synchronously with acquiring of the first and second images, in such a way that, in each image of the reference area, illumination of same type is aimed at the reference area, wherein the images created of the reference area are used to determine the position of image areas corresponding to the area of the subject in the first and second images.