From Works of Wonder:
"Occasionally, I'll use a model in the course of painting an illustration. In this case I decided to use a photographer who worked about an hour's drive from my studio. Rather than waste the time traveling, I sent him the preliminary drawing I'd done and told him to duplicate the sketch in a photo. When he received it he called to ask, 'Why are you bothering?' Sometimes I say the same thing! But in retrospect I realized that using the model to reassure me that the lighting and proportions of the pose were conceived correctly. Sometimes they are not, and I'm glad for the chance to correct the error. Occasionally I'm right, and the photo is wrong! Distorted perspective and odd quirks of positioning can sometimes lead an artist astray if he or she follows a photo uncritically."