if you shove copyright Apple inc (or whtever the actualt company name is) into the bottom corner or somewhere u should be fine. whether it is 100% legal is questionable but acknowledgment means u will most likely not get botherd
Its not quite original to say the least... but Apple's legal department has better things to do than hunt down every website using their photos from /library/desktops/
I'm pretty sure that's not true. Apple have almost certainly licensed that image for redistribution with OSX, but it is almost certainly copyrighted. Buying a copy of Leopard does not give you any redistribution right, or even any right to use it outside of the OS. Whilst Apple are unlikely to chase individuals over this image the copyright holders may well.
Whilst I can't manage to find a link I'm pretty sure there was a case a few years back where someone re-used a stock image supplied with Windows and the original copyright holder took them to court.