I'm slow to watch some of the movies that are released each year, even though I really want to. Yesterday, I watched Rumor Has It - a movie that came out in 2005 with Jennifer Aniston, Kevin Costner, Mark Ruffalo, and of course Shirley MacLaine. The premise of the story is that a woman discovers that the book and subsequent movie, The Graduate, is based on her family. This struck a cord with me because the book I'm working on now pulls from some of the emotional experiences I've been through, some more recent than others. While it is definitely a work of fiction, the idea was born from a series of emotional traumas in my own life, something I suspect from which most fiction is born.
So, when is fiction truly fiction? I'm sure there are court cases, but one measurement is offered to be whether or not something is said or depicted that is an out-and-out lie and causes someone financial harm, or at least this is how it was explained to me. So, if you have for example court documents or letters written by the individuals who might resemble your characters it becomes much more difficult for anyone to sue you and win - and it could generate a tremendous amount of publicity.
Back in the 1990's there was a law suit by the Andy Warhol estate against an artist who took one of Warhol's drawings and morphed it with the new morphing software that was becoming popular. The ruling went in the artist's favor I believe because it was found that the painting no longer looked like the original but that the artist had created an significantly new work.
Writers often worry about someone stealing their ideas but this is less likely and most court cases have not found in favor of the person suing. Ironically, J.K. Rowling has been on both sides of this issue. Most recently, she was accused of stealing the idea for Harry Potter for a second time.
But she has also sued someone for using not only her idea but her characters in an unauthorized Lexicon.
It's important to understand that for the most part idea's cannot be copyright protected but the individual execution of those ideas can. This is different than someone obtaining a patent for an invention. Titles also aren't copyright protected which is why you'll see the same title used by different authors.
Still, these are all issues to worry about if and when they happen as long as the writer is not actually intending to plagiarize someone else's work. Taking one's own experiences in life as inspiration you'd think that this would avoid the whole plagirism issue but most authors will tell you that fans often tell them that a character or two is just like someone they know.
I guess it really is a small world after all.