I hope this is not hijacking a thread.
But I was trying this find a solution for this too. I have seen this working with other vBulletin fora.
It should be possible to add an image to a prefix, and more people in different threads have been saying to use the 'rich edito' when adding a prefix.
But I cannot find any rich editing option at all when adding a new prefix.
The admin just allows you to add a prefix set, a title and display order.
Like here:
http://i27.photobucket.com/albums/c1.../Picture14.png
I have seen more people suggesting to use the rich editor, but where is it? *^__^*
Can anyone tell me?
Kind Regards,
M
EDIT: Argh never mind! 
I tried some more and I did find it in the end. Was just a matter of reading better.
First to create a set, then to add a prefix to the set, and when you do that you can rich edit.
Sorry for the bump.
It works fine now.