Money quote from a lawyer's letter from Joe McGinniss to the Discovery Channel:
It has come to our attention that the first episode (titled “Mamma Grizzly”) of the above referenced television show ... contains unauthorized videotaped images of Mr. McGinniss which were obtained without his knowledge or consent... Mr. McGinniss was not asked if any production crew could videotape him as he read a book on the secluded deck of the house he was living in at that time. He was not aware that any camera crew was in fact videotaping him. Mr. McGinniss had a reasonable expectation of privacy under those circumstances.
The mere taking of the video therefore gives rise to an actionable claim for invasion of his privacy. The publication of the video on your website and in the television show constitutes an additional wrong the unauthorized use of the likeness of Mr. McGinniss. Finally, the manner in which Ms. Palin describes Mr. McGinniss in the episode is defamatory: Mr. McGinniss has never invaded the Palins’ privacy, contrary to the many statements made by Ms. Palin and her husband, both prior to this television production, and now repeated in the episode referenced above.