You can load an image... You will see under that where you can link to an off-site image or upload an image then it gives you the option to insert. It may require bbc code and not html. Still playing with it.
There are new signature rules, I assume the same goes for avatars. Basically Jeremy's trying to get all the signatures and avatars hosted locally and with as small sizes as possible so that pages load fast. Animated GIFs are generally much larger file sizes than normal images, hence not allowed.