It's not easy to scorch a negative, pigment-free image onto cloth that when analyzed using a NASA terrain analyzer reveals a 3-dimensional image of a human body. In fact, it's such a difficult task that scientists today are unable to do it or provide an explanation for it. The medieval forger must have been very talented.
The statement that it can't be reproduced is absurd. Artists make three dimensional drawings all the time. AB blood and body fluids still exist.