Just kind of thinking aloud here. I was thinking about the bandwidth overhead for applications which use the API to set avatar or profile background images and had an idea.
How about allowing an application to register an uploaded image with some sort of id or handle and then be able to set the avatar or background image to that id? e.g. app foobar uploads an image and registers it as "bg1" it can then make calls to update several accounts and set the profile background image to "foobar:bg1" or similar.
