I had alittle read about fanfiction legal issues.
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Legality
Main article: Legal issues with fan fiction
Due to the modern definition of fan fiction as derivative works, there are many legal issues involved with fan fiction, most prominently (but not exclusively) arising under United States copyright law.[25]
Several prominent authors have given their blessings to fanfiction, notably J.K. Rowling. Rowling said she was "flattered" that people wanted to write their own stories based on her characters.[26] However, Anne Rice has consistently and aggressively prevented fan fiction based on any of her characters (mostly those from her famous Interview with the Vampire and its sequels in The Vampire Chronicles). Stephenie Meyer has put links on her website to fanfiction sites about her characters from the Twilight series.[27]
Most authors, however, seem to turn a 'blind eye' towards fan fiction - not actively approving it, but not discouraging it, either.[citation needed] In some cases this tolerance may be due to the fact that, due to the internet, preventing fan fiction from being published would be an expensive and almost impossible task.[not specific enough to verify]
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I guess it really boils down to the fact, if the owner of the copyrighted material thinks its okay or not.