For the discussion of general and orthodox history from the advent of writing up to mid 20th Century, i.e. 3,200BC up to World War II.
No, it could not have been anything human. The face is not realistic, but shaped according to the conventions of Byzantine art. More importantly, it's a flat image. Linen does not lie flat on real human bodies. It would bend around a real body and the result would be a distorted image when the cloth was laid out flat again. This is clearly an artificial image, we just don't know the method used.