| > At a time when the idea of a photo negative was entirely unknown It was not called a negative until the 19th century when photography came about, because before that a photo negative wasn't a thing. Before that it was just a "painting with light and dark reversed". > when there are no other examples of negative images, or even any mention of the idea of making such images There are many examples. See woodcuts, for example. The concept of creating the negative of an image was common. > why would the fraudsters seize on the idea of making their fraudulent image a negative? Because they, and the intended consumers of their piece, were not stupid and all were aware of the pattern that a person would leave on a cloth. Presumably it was not more difficult to drape a cloth over a body and observe the staining pattern then than it is today. > You would expect a straightforward image. No, you would expect a straightforward image, because photographs weren't invented until many centuries later, apparently. |