That's true, and would work on a web site with the code embedded, I have such a script somewhere, but you would still stuggle I think to call it remotely onto here, the [img] tag, only allows for known image formats to be used, the old trick of sticking a url to a php generated image no longer works.
heh, you could have an animated gif with a 24 hour time delay between frame changes I suppose, that way it would change at least once a day, don't think the time change add's anything in the way of size to a .gif. Make a 30 frame image, with a time span of, oh god I dunno whats 24 hours broken up into milliseconds and image link that.
Extreme way to do it I guess.
Or another way you could do it is, ummmm upload a shit load of image to a server, and errrr, go edit your profile at the start of each day to change the image link, would take what , about 30 seconds ?
Either would work, have fun , I can't see image sigs any longer, should try turning them off the boards look lovely and clear without them on