There is more controversy among those who think the Shroud of Turin is authentic and more controversy among skeptics than there is between the two groups. This observation is clearly demonstrated when we think about all the proposed possible ways the images might have been formed. If there is one thing we can conclude from this it is that in reality no one has the faintest idea about how the images came to be on the cloth.
3 reasons are given why Camera Obscura is not viable.
1) The cloth is from a later date. BUT, Leonardo is not dumb. He would have used older cloths even those suspected from Palestine which could have easily have been provided by his employer, the Roman Church.
2) The obscura image doesn’t produce a 3d rendering. In fact it does as shown here,
http://www.youtube.com/watch?v=lp7687Mk4yI&feature=related
3) No chemical light sensitive substance could be found. The reason is because such chemicals long since evaporate and are not detectable once they cause a burn.