A friend has asked me to help him with a rotating forum avatar - that's my description and not his!

On a particular forum, he wants to specify in his user profile his avatar as http://some_php_host/avatar.jpg and have that web host deliver one of about 5 avatars at random or simply have them rotated in a pseudo-random manner.

I've done a bit of Googling and I keep on getting explanations on how to rotate banner ads and the suchlike, none of which is really what he wants.

Bearing in mind that I'm pretty much a php novice, can anyone here suggest something ready-made that more or less just needs uploading and configuring, please?

In an ideal world, there would also be a simple avatar upload interface too, but that really is the icing on the cake!