Last Friday I was at the 2012 New York Comic Con with a Paul Belliveau, who is an animator. He knows an actual comic book artist, Chris Batista (who is cool enough to have a Wikipedia page), who has worked for Marvel and DC, from their time in school together. It was a lot like the Phoenix Comic Con from May, when ICA was in Phoenix, except that it was bigger and with fewer personalities (since Phoenix is so close to LA). The cosplay was awesome.
One thing I noted in Phoenix was all the artists who make their own artwork of Marvel and DC heroes, either rather awesomely or with their own differencing style. Although Marvel and DC are not people and did not make any of these characters, the two companies own the rights. How was this allowed? The answer is that it's expected and tolerated to a small extent.
The same was true in NYC: there were tons of artists with their own artwork that had Marvel and DC figures in it. But, for Chris Batista who had actually worked for Marvel and DC, it was a little different. He had actual layout pages (I am not sure of the exact term), that is, the large format black and white layout pages that he had drawn, and was offering them for sale (and they are for sale here at The Artist's Choice website). These are the original artwork before they are colored by the colorists.
There are a couple of things to keep track of here.
Copyright, in the US, is based on written law that specifically says... "To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries."
"Work for hire", which most creative people are hired under these days, destroys a creator's right to copyright completely. Comic artists are hired under work for hire. Work for hire sucks.
The comic book that you get at a comic store is the creative work of many overlapping people. It may include writers, artists who work in black and white, and colorists, among others. Copyright and personal ownership rights here are not straightforward (sadly work for hire wipes all of these considerations away).
Yet, Chris has the right to sell this artwork (it's just the black and white, as you can see on the website). This is art that he made, and he owns it, yet Marvel or DC owns (or "owns") the characters. That makes my head spin a bit.
One interesting thing I got out of Phoenix was when I asked a fez making company about their fezzes, as some had a British police box on them, which happens to be the Tardis from Dr. Who. The person at the booth said they contacted the Dr. Who people, and they essentially said "As long as you call it 'a police box' we are very happy to have you do it all you like, since we don't own that -- if you call it 'the Tardis' then that gets into licensing and all that, and it's easier for all of us if that doesn't happen -- but, since no one owns the rights to the image of a British police box, you can use that all you like and don't need to ask permission of anyone, although we are really glad you asked and that you are fans."
So, I don't have a snazzy conclusion, but, there's all that.