If you're compositing renders made against a black or white background into a background image, you may find that it adds to the photorealism if you use Layers, Matting, Remove Black Matte or Remove White Matte. This will clip off the remaining background pixels from your figure. The other thing I do when I want to add shadows is to copy the layer the figure is on, fill the copy with black, move it so the layer is below the figure's layer, use the transform tools to distort it so it looks like it's on the ground plane or whatever, do a Gaussian blur to soften it, reduce the opacity to around 50% or whatever looks good, and it makes a pretty good shadow as long as the light is coming from behind the viewer, so the shadow extends into the picture. If I need a shadow to be in a different direction, I usually do a separate render from a camera position pointing from the direction of the light source. Then I do the same operation, filling it with black, etc. to create a shadow that appears to be geometrically correct. Gromit