What are characteristics of shadows in an image given an outdoor setting from an image processing point of view?
The edges of the shadows are crisper where they are nearer to the shadow caster.  Also, since the sun is so far away, beams of light are essentially parallel when they reach us, which means that shadows from sunlight are basically orthographic projections of the shadow casters.  Also, if you knew an objects dimensions and saw its shadow on something that you knew the slope of, you could probably calculate the angle of the sun, and so maybe could calculate what time it was, and maybe something about the season or latitude??