If you look at the original shroud, you see the faint outline of a tall man with some distinguishable features. Let's assume that the guy who made such a thing would have been able to sell it for $500.
If you look at the negative of the shroud, you see amazing details about the position of the hands, the exact locations of the wounds, etc. (in other words, the shroud is actually the negative and the "negative" of the shroud is the real photograph). If someone in the 13th century truly had the ability to create such a thing, he would have been able to sell it for $500,000 instead of $500.
Logically, it seems that anyone with a profit motive would not have created the shroud as it was seen in the 13th century if he had the ability to create it as it was seen in the 20th century.