The Shroud "strikingly resembles popular images of Jesus" because our popular images of Jesus (going back to at least the 6th century) are based on the Shroud!
And then he adds:
See below images of Ian Wilson’s three examples of "artistic likenesses of Jesus originating well before 1260 … all strikingly similar to the face on the Shroud":
You should go over to his site to see the pictures in a viewer and read notes that Stephen has added. They are: