During an interrogation, they show a very clear, printed picture of the murder. After this, they go to a crime lab where supposedly the sharpest picture they have of the scene is very pixelated and they need to enhance it.
The dead photographer apparently stored his exposed film in a makeshift cooler under the passenger seat in his car, along with several ice-packs. The film seen removed was without a protective plastic container, and therefore exposed to the condensation which would have formed on the ice-packs. No professional photographer would risk destroying his pictures like that.
Calleigh says, that a gunshot is hot dust and carbon monoxide followed by a bullet. It's the other way around. First bullet, then gas and other ejecta.
The CSI team finds an empty pack of chocolate under a tree, and they deduce the victim was on this tree. But we saw earlier that the night before was stormy and windy in the same area, so the pack wouldn't stay lying under the same tree.