The invention relates to a method for extracting marking patterns in relief on the surface of the sidewall of a tyre, comprising steps wherein: the three-dimensional image of said surface of the sidewall is captured by associating, with each pixel of the image, a greyscale value proportional to the elevation of said point in relation to said surface, in order to obtain a starting image (f); a series of successive morphological openings of the image of the starting surface (I), (II) and (III) are carried out iteratively by means of linear structuring elements of successively increasing sizes, oriented in the circumferential direction; the value of an image obtained after morphological opening with a structural element is subtracted from the value of the image obtained after morphological opening by means of the structuring element of an immediately smaller size (IV) and (V) in such a way as to obtain a succession of images flattened by the difference, initialising the procedure by the subtraction of the image obtained by means of the smaller-size structuring element from the starting image (f); a thresholding of the images flattened by the difference is carried out in order to obtain binary images (VI), (VII) and (VIII); and a set union is made of the values of each of the binary images to obtain a final binary image wherein only the marking patterns appear in relief (IX).