Adding graphical background to posts

Hey all, I’m a new wordpress user.

In the process of creating my own theeme, I have come up with an idea to add a graphical background to each specific post.

http://www.gd-gaming.com/wordpress/
Example: On the right side of the website, I have a list of players (These are all individual posts that are pulled to the frontpage)

I would like to add a team background to each of those small boxes..

So in a Patriots players box, there would be a patriots logo.. So on and so forth.

Anyone have any idea how I could go about doing this?