I've taken a photograph of each of my subjects in my so-far 157 days of making a daily illustration, which serve a few purposes. First, I can see a history of the actual vs painted item and that's just fun. Second, it is MUCH easier for me to draw a subject that has already been 2-dimensionalized (not a word!) through the flat image. And, third, it is sometimes night when I get down to painting, so a brightly-lit reference is very helpful.