What legalities are involved with drawing portraits of celebrities?

Answer 1

As far as I know, none. Once you reach true celebrity status, your likeness becomes public domain, and you cannot sue for someone using or creating your likeness without your permission. However, it must be an original rendering. If you recreate an existing picture or scene of the person, you are actually violating the copyright of the photographer who took the shot, not the person the shot is of.

Answer 2

You can draw a picture of anyone that you want. There is no limit on that whatsoever. The complicated part comes when you actually use a photograph itself taken by a photographer with the rights to that image. If you are drawing the likeness from a photograph, it must be discrenably different from the original, which is where the gray area comes in.

When it comes to editorial use, like political cartoons, you can pretty much get away with anything. You can draw the poresident in comprimising positions with woodland animals if you want. It's all covered under freedom of speech. I'd say you have very very little to worry about.