Unique images for each different forum
 

hello everyone and excuse my poor knowledge on all of this, i'm sure this question has already been asked a lot of times, i just couldn't really find any when i tried searching.

i'm looking for a plugin or just some sort of setting to make each topics in main forum has unique images. i thought http://forums.explosm.net/ would make a good example, i really wanted to have this look for my forum for a long time and actually that page that made me switch to vbulletin.

hope someone can help me out.