adding background image to a post
 

hi everyone

i noticed that in a forum you can add a background image to the post
i tried in my forum but i got nothing

the code for adding the background

Code:

[align=CENTER][table="width:100%;background-image:url(http:// );"][cell="filter:;"][align=center]
[/align][/cell][/table][/align]
what do i need to enable this feature in my forum?