I had three stories running throughout my adolescence. Sometimes they crop up again, to fill space if I'm very bored. I would take characters from movies I'd seen, and comics I'd liked (one of the stories was My X-men) and then use my own plots etc. They were very violent and repetetive. I always asked people if they did anything like this and nobody ever did...it was always under my control, however, to pause, and restart, although I sunk into them everyday, to ease boredom at school and anywhere else.
I harnassed those powers and put them into writing books back then, and I'm still a writer now. Even back then I knew I couldn't just "write" my stories because of their visual nature, everything being stolen...my best advice is not to read fanfiction on the internet. Begin reading novels, fantasy novels or whatever you like, if you like star wars read those books, or get into a big fantasy series. Do your stories involve a lot of Hong-Kong action, intensified comic-book violence, sex-stories? I bet they do...read novels, and you'll find instead of "images," sentences and narratives will "possess" you. Suddenly you will have awesome power to write, which anybody respects.