Use sticky background and post type image

How can I make it so that special post types that have their own icon (image, link, etc) show their icon when the post is a sticky? I am using custom css to use my own images, but when I sticky the post, this happens:

http://img708.imageshack.us/img708/955/xm9s.jpg

Here’s my custom css code:
article.format-image { background-image: url(images/picture.png); }

I tried adding no-repeat but then it doesn’t display it at all.