You have to set your avatar link as a direct link to the image hosted on geekavatar.
There are 3 different ways to set your avatar, but only one is working :

• Upload an image from your computer to the forum. This is not the working one.
• Upload your image from an external link to the forum. This one will upload ranomly one of your images, so your avatar will not change on every page load.
• Link your avatar from an external link. This is the one you must use.
  Note : some forum admins disable this last option to prevent avatars to be too big.