What are characteristics of shadows in an image given an outdoor setting from an image processing point of view? I'm wondering what basic characteristics of shadows are. I'm looking from a camera image/video processing point of view. I'm considering the case of an outside scene in direct sunlight.

These are the characteristics I could quickly come up with, but I guess there are more.


There are strong edges on the shadow borders
The shadow is ‘darker’ than the surrounding area
The shadow usually ‘deforms’ when an object is rotated
Due to absence of the primary lighting in the shade, the color tends to be dominated mostly by the main diffuse lighting source (which is in most cases the sky --> blue)


I'm wondering which other characteristics I might miss.
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??