This is all very interesting as I sometimes love postulating. Next, I am certainly no expert but do have varied interests, so...

A while back I watched a documentary on the shroud of Turin. They were all working on how old it really was and how it could have been made. The connection? Many scientists agreed that in the early 1500's it was well known how to permanently stain cloth using metallic salts and _light_. They also were experimenting with camera obscuras. They demonstrated how the shroud could have been produced using 16th century chemical and optics and were successful. There even was some mention that DaVinci may have produced the shroud as he was in the area it was first introduced and had the knowledge.

So the first photograph? How about the Shroud in the mid 1500's