A judge has ruled that the use of the John Lennon song Imagine is okay in the context of the film Expelled! Yoko Ono and the sons of John Lennon had sued to have the film distribution stopped because of what they deemed unauthorized use of the song. As the Reuters story notes, though:
But on Monday U.S. District Judge Sidney Stein found in favour of the filmmakers based on a "fair use" doctrine. "That doctrine provides that the fair use of a copyrighted work for purposes of criticism and commentary is not an infringement of copyright," the judge said.
I am sure that there was considerably more to the ruling but that quote seems a tad vague. I have little to no doubt that Weird Al Yankovic needs the okay of a music publisher before he skewers a song. Having said that, Yoko Ono has been living off of John Lennon's image for decades with little music output of her own, so I am not that sympathetic.