Putting A Image In the Background In Wordpress

I would like to put a image for example the superman logo in the background "under" my text in my post on each and every page. How would I go about that?

Also what would be cool if I could get the image to scroll with the reader as they went down the page.

Thanks

 

I can help you do this. PM, i'd be glad to help you in coding this up for you.