I think it's a both a bit too much in general, plus a source of potential confusion, although I haven't used an N900 yet to see exactly how multi-choice things work.

If you add a few image files does it just quickly flick through them, or can the user set a time for how long to pause on each image? In any case, it doesn't sound terribly useful. As with videos, I can see the value in picking a single image for boot up, but not several.