A method comprises projecting a light and shade pattern defined by preset optic parameters through a body, detecting an image of the light and shade pattern through the body to obtain a detected image, processing the detected image to highlight any irregularities of the light and shade pattern in the detected image; an apparatus comprises a light-source for projecting a light and shade pattern defined by preset optic parameters through a body, an image-detecting device for detecting an image of the light and shade pattern through the body to obtain a detected image and a processing device for processing the detected image in such a way as to highlight any irregularities of the light and shade pattern in the detected image.