Contact your legal advisor. Particularly one who is specialises in trademark and copyright law. They will walk you through what you can do, what you can't do... and show you how to work within the odd grey areas that a lot of Authors work within. Stay within those 'grey' areas and you're pretty safe. Keep it to a minmum, though.
Keep in mind there are provisions within copyright law that will permit the use of third party images to be used by Authors under specific conditions. Stay within those laws and you will be OK.
-Windebieste.