Paul Vignon (1865-1943) was a French Professor of Biology  and an artist . He discovered there were twenty unique features of the Shroud that were found in these depictions of Christ from the sixth century onwards . But Wilson reduced these to a more definite fifteen.  Some of these features are merely wrinkles and imperfections of the fabric of the Shroud and artistically make no sense.  Yet the artists slavishly copied these features found on the Shroud, including the imperfections.