Marvel.com Copyright Wallpapers?

Been having an arguement with someone about if wallpapers on Marvel.com are allowed to be used in tags/sigs and other graphic forms.
The person says "no you can't use it unless you get permission directly" but I know many people here use Marvel wallpapers and make renders etc. out of them.
I need to know if they are allowed to be used to make sigs and officially shown to the public, through forums etc. like GR.
If they are allowed I need a good arguement ASAP.

Thank you to whoeva can answer, and I don't want OPINIONS, I want FACTS!

 

You may use them if you're not using them for money (commercially)

 

it's considered "fair use" in the US.

 

most of the time yuo need permission if you make money off of it, or its used publicly

 

However in private cases you may use it for free obviously so there is no copyright on it until you're using it as your personal computer wallpaper

 

The fact is you should have contacted Marvel.

 

oh yea right ^