A simple guide to help those who don't know how to give credit. :)
The most common and prefered way to give credit is in the keywords and, just recently, in the icon's comment section.
Giving credit is easy and doesn't take long to do. By giving credit, you help support the person who put their time and effort into making them. It also tells other users where they can get spiffy icons. :)
First thing you need to do is get to the Edit User Pictures section. You get there by going to Manage and then User Pictures.
Then you simply put the appropreate information in the keywords or comment section. The second icon shows an example of crediting that will link to the maker of the icon. I personally think that's the best way to go. The third icon shows the credit in the keyword and where the images came from in the comment section.
In the end, this is what it looks like. (Image is a bit fuzzy because I shrank it some ^^;)
Sometimes LJ artist let other users use their images for icons. I feel like both of them should get credit. This is a possible way to credit both the LJ artist and icon maker. :)
Guide to Crediting by emmysdream. She goes into a few details that I didn't know about, so you might wanna check it out. ^_^;
Hope that helps! If you have any questions, feel free to ask and I shall try my best to answer them.