A lack of integrated forum avatar hosting is one reason I've never bothered with one here[1]. The only SMF-served forum I've bothered avataring on in the past also had file-uploading capability for within posts, so it may be that the one (technically could be very limited on resource impact) can't be done without the other being enabled (we'd have DFFD-type stuff and more being uploaded/using up bandwidth). And/or, with the fairly minimal set of moderators/administrators at work here, Tarn doesn't feel like he could keep on top of any legitimate complaints re: inappropriateness/copyright/whatever.
And I've used a number of free image-hosters (e.g. tinypic) before, and sometimes after, they messed about with their workings to possibly nix their usefulness as an avatar-holder for this scenario. Yes, it'd be so much handier to be localised (no worries of "Image broken", this side of bay12forums themselves breaking, or maybe being broken by a major version change/migration) but understandable if it is never made available. And there are far more free-hosters out there than I can be bothered to look up, so maybe (if paranoid about loss/intentional-degredation of service) you could even upload to two types, ready to switch from one to the other should the first suddenly exhibit issues. You'd do the same (but switched primary/backup) on a different forum, to discover when the 'backup' fails first and a new backup (or primary, on the immediately affected BBS) needs to be implemented.
(Well, I'm sure much of that is so obvious it didn't need to be said, but it looks like I did anyway.)
[1] Though it is really secondary to my utter indecision as to what to use, never lacking in ideas, and even having put pencil-to-paper pixel-to-canvas a few times. I have locally uploaded a relevent graphic to at least three other fora (though nowhere else am I 'Starver'), and used the "build in place" constructor on a fourth, across at least two decades of web-forum[2] use, out of an uncounted total number of unique logins. But the point being that I let my username represent me more than a potentially inconstant and changing[3] avatar image. Which makes me boring, I imagine.
[2] And then there was the X-Header embedded and encoded 'avatar' bitmap I'd used on Usenet posts, before then, though that needed a compatible newsreader plugin at the other end to appear on remote machines, so was not really the same.
[3] And not even in the way yours is, Bumber, cycling/randomising images from a pool, per each request, via however your dedicated image-hoster lets you configure these things.