image.php only works if the user has a custom avatar, and the reason that you're having that problem is that the browser caches it. To get around that it needs to have the "avatardate" field as a parameter. We discussed it a while ago in this thread:
http://www.vbulletin.org/forum/showt...ight=image.php (I think the final working code is in the next to the last post).