TheFairUseDoctrine, copied and pasted below from the US Copyright Office stipulates that it is legal and permissible to use copyrighted material under thefairusedoctrine for purposes of parody.
Copyright experts we advised with before posting the song told us in no uncertain terms that we were within our rights to usethe song because we did so in accordance with theFairUseDoctrine.
Regarding Napster's claim that its users were not infringing copyright because sharing copyrighted musical compositions and sound recordings via the Napster service is protected by the"fair use" doctrine, the court held that the four fairuse factors in the Copyright Act tip the balance in the record companies' favour.
David Cameron pointed to the " fairuse" doctrine in American law, which he said had allowed companies like Google to flourish without fear of infringing copyright.
When it is impracticable to obtain permission, use of copyrighted material should be avoided unless thedoctrine of fairuse would clearly apply to the situation.