background image per post

So I want to add a background image to EACH post.

Not necessarily in each post that I make. Let’s say I was typing a post on Barrack Obama, then a photo of Barrack Obama or the white house would go as background. If I was doing a post on Disney World. I would put a photo of the Disney castle. Get the point?

Is there a plugin that ca do this? I don’t like touching the code because the change I make, might disappear during next update.

Obviously the photo would be edited so the text on the post can be read.