We're not Wikipedia, so we have no intentions of telling you what can and can't go into your userboxes. Since we're a fan site, we expect you to follow "netiquette" however when you create them. We have no other restrictions on what can and cannot go into your userboxes, but we'd prefer it if you tried to keep your userbox images to a size of 45 pixels - no more or no less. This is just so they all fit well.