Another way to do this is like I do it... different usergroups have a different badge or medal next to their names... admins, mods, premium, and ultra-premium users all have their own graphic. You can visit my forums to see it;
http://www.juot.net/forums/ They show up in the post bit and also in the who's logged in section at the bottom of the main forum page.
To do this just add the HTML <img> code to the "Username HTML Markup" in the usergroup editor. If you want it before the username put it in the opening box, if you want it after the username, like me, put it in the closing HTML box... make sure you add the border=0 attribute so you don't get an ugly border in Internet Explorer. If you are going to use a different image for each user then this is a pain but in that case that is what avatars are for. My guess is you just have a handful of images so usergroups is probably a good way to go... make a custom usergroup with the same settings as registered users with the img tag in the proper "Username HTML Markup" box... make sure each user's "Display Group" is set to default and the "Primary Usergroup" is one of the new ones you created.