I dare you join this challenge, friend. I do this on a regular basis. And it works. It may seem like a radical approach, but our brains only learn the hard way. Instead of teaching our brains that porn equals pleasure teach them, that porn equals pain. Look up "Pavlov´s Dog" if you want to learn about the mechanism I want to use. Thinking about P? Then pinch your ear. Indulging in memories how awesome this and that was? Nude pictures flashing in your mind? slap your face (if no one is looking). Your body needs to learn that porn is painful. Of course your body should not be damaged when doing this challenge, so don´t go emo on me and start cutting yourself. Just do things that hurt reasonably much and don´t do any real damage. Like I said pinching your ears, slapping you face on a good spot. Of course you should only do that if you are alone, otherwise others may think you are a mental case. Lol. Give it a try if you can endure pain.
I've tried these kind of techniques before, similar to that of teaching a dog not to bite, using your own power and weaknesses against oneself. Self-restraint is more important though, it shouldn't be a game/challenge, because what you lack is discipline.
Only by truly embracing the goals of the future and what type of person you want to become, can you restrain yourself with enough discipline to stop PMO altogether. Picture the future. Write down your goals. The feelings you want to experience, the feelings you want to share with others, the new friends, stronger bonding with family members and a general better sense of well being. Look at someone you admire, and think for a moment, what do you think they do in their spare time. They use restraint to maintain an image and level of confidence.
By sacrifice. Sacrifice free time, sacrifice doing cool but useless stuff. Sacrifice old habits. Sacrifice being lazy. Sacrifice procrastinating.