Don't know where I should post this, but I thought this place was the most fitting. My question is, am I allowed to use a photo as a background for a composite...or is it against the law. Help appreciated!

I'm sure its fine!

They have to put that copyright warning on it so that the pictures can't be used in print publications without permission.

I wouldn't have thought anyone would have a problem with you using their shot, but then again it's personal preference of the photographer 

Use of a Copyrighted artwork for ANY purpose other than that which the artist intends is subject to the Laws of Copyright.  Even if you do not "make a profit" from it's use, you still do not have the right to use it unless you ask for and recieve permission. 

Abuse of this is absolutely FLAGRANT on the web.

The odds of formally getting "caught" for the reposting of a copyrighted image are very, very small....... even less if you are doing so in a non revenue producing venue.  Does the lack of odds for getting caught make it legal or "right"?

This is at least as large a MORAL issue as it is a legal one.  Is it fair to the original artist to steal his or her work and use it as your own?  How much content can be lifted and still be considered under "Fair Use"?

HOWEVER, while YOU might not be a "commercial" venture,  the site on which you post the your "lifted" content MIGHT be considered a commercial entity...and THAT site then becomes the target because of the copyright infirngement.  Then you get the issues you see with places like "YouTube".

Food for thought.

best,

.......................john