Crediting icons in your userpics is important because it allows other people to find me and my graphics! If you don't know how, here's a quick step-by-step guide to help you out!
1) Add desired icon to your userpics.
2) Put in a Keyword so you can find this icon easily when posting a comment or entry in the future.
3) Under the "Comment:" section add "Credit goes to <lj user="USERNAME GOES HERE">
4) Click the "Proceed" button.
5) There you go! You've just credited! The result will look like this:
If you want to make doubly sure it linked properly, go into your user info and click your userpics again.