How do I obscure paths in nginx?

How do I go about obscuring paths to images? When someone views source of an image, I want the path to be obscured. I also want the image to be a background in CSS.

I realize that people can still take a screenshot of my image which is okay, but if anyone types the words on my images it's proof that it is mine since I will not be providing text for my work, just images.

Make sense? Is there and app for this? ;-) Or is it just a simple nginx rewrite?