I rely on photographs for reference while in my studio painting but I often have to remind myself what the camera sees and what the eye sees in the outdoors are very different. The camera averages the exposure of a landscape and in so doing, the sky may be washed out in order to keep the trees from looking too dark. Another problem with photos is that it looks at the entire picture at once. The eye look and focus on small areas and will adjust itself to see into that area. For instance, I might look at the shadow under a tree and my eye will dialate to see the detail there. A photograph won't do that because it sees and exposes for the entire scene. Our eyes move around and quickly expose themselves to small areas giving us a clearer picture and more information that a photograph can produce.
One photographic solution is to shoot multiple exposures of the same scene or use photoshop to create several different exposures of the same photo in order to see more clearly into those areas which are too dark or too light. That of course will also leave some parts of the photo overexposed and others underexposed leaving the artist to put it all back together with it's appropriate real life values.