Heya guys, so here we go!
Let's say that we want to give this picture a nice shadow
We throw it in photoshop and we give it a random background, I went for black with a white pattern so you can see the shadow.
Then you duplicate the worm's layer:
You change the HUE of the new layer you made (the shadow layer)
Then you have the shadow, move it a little so it looks real:
Change the opacity a little so it looks real
And then you can easily make something funny like this:
If you want to do this on a human so it looks real make the shadow a little closer to the render.
Ciao,
JD