Blizzard accidentally released the wotlk forums but quickly took them down. They never got rid of the images though.
They have the same name as the bc ones but are in a different folder.
BC image:
http://forums.worldofwarcraft.com/im...ow-base-cs.gif
Wotlk image:
http://forums.worldofwarcraft.com/im...ow-base-cs.gif
Here is a custom stylesheet to see the wotlk forums in Firefox:
WoW forums wotlk theme | userstyles.org
Sometimes you have to load the forums without the stylesheet first to get the images to load.