Originally Posted by
Psykoticrage
First save the image somewhere in the wow folder, for reference i put mine in world of warcraft\interface\kgpanels images, just outside of the addons folder.
/kgpanels config
Then go to Art Library, on the right side where it says artwork path i would put in \\interface\kgpanels images\image.tga
In the Artwork Name box you can put whatever you want so you will easily be able to pick that image out from a list if you decide to import more than one, like circular gradient for example.
Make sure Artwork Type is set to background, and hit the add button. If all went well you should be able to hit the + button beside the Art Library tab, then the same with the Backgrounds tab and your image should be in there.