[kh99]

I'm not an expert on this (or even very knowledgeable), but I think it's probably a browser thing. You can configure your web server to set an expiration time for certain file types, like image files, but I think the browser can still do what it wants. And I think browsers cache images even if your server isn't configured to set an expiration. So probably your browser is checking for images being changed every time you load the page, and your admin's isn't, or something like that. I think it's also possible to configure your web server to tell browsers not to cache any images, but I don't think you'd want to do that. When you change a "static" image that isn't meant to change often (like whos_online or stats gifs) then it might take a while for everyone to see the change, but they will see it eventually.

The avatars are another story. An avatar url should really contain a revision number as a parameter if the user has a custom avatar, that way if the user changes it the revision number will change and the browser will see it as a new image. But even if you don't include the revision number, it will update eventually like the other images do.