The main page is subject to the same rules as the rest of Wikipedia. It's also subject to this wonderful stuff called "Common sense"

The policy is quite simple. Where we can, we use free images. Where we can't, we're willing to use fair use images. Now, generally, we like the main page to set a good example, so we try hard to avoid fair use images there. But don't confuse discouraged with prohibited.

If we should happen to have a fair use image on the main page (ala, [[Jim Henson]]) and you know of a free alternative, by all means replace it. However, our policy does *NOT* give you license to start an edit war on the main page, or vandalize it by overwrite the image with a blank one just because you don't like fair use.

See? Common sense.

--Mark.