Animated images were allowed to use as avatars but because they are annoying images, theymos disabled it. After that announcement, you can not upload and use animated images for avatar.

Years ago, newbies can wear avatars too but after a forum hack, it was disabled. There are glitches and you sometimes can see newbies wear avatars or users with animated avatars. They will lose those avatars if they remove it or upload a new image.