Does anyone of this book called, The Relaxation & Stress Reduction Workbook (New Harbinger Self-Help Workbook) http://www.amazon.com/Relaxation-Reduction-Workbook-Harbinger-Self-Help/... ?
I have an old edition of this book, and it describes a technique called thought stopping. I have successfully used thought stopping for stopping thoughts and images of horror movies.
At the most basic level, the technique is to call out stop whenever an image flashes in the head, and then immediately focus attention on something else. Calling out stop first is aloud, and with practice, even mentally calling out STOP works. Saying this from personal experience. You can also wear a rubber band on the wrist, and snap it(gently) while calling STOP and substitute a better thought.
Also, quit saying, I will quit porn, instead say, I will substitute porn with____________(some healthy habit). You cannot stop thinking of green elephant if you keep saying, "I won't think of green elephant".
By saying, I will quite porn, your focus is still on the porn. Focus where you want to go, that's away from porn, by substituting porn with something healthy. e.g. running.
Please check out the book, there're many more techniques in it, and post back if it helps.