The moment you have a sexually stimulating imagine in your head, blink both your eyes as fast as you can for 10 seconds!
If that doesn't work, then blink one eye, then the other, and alternate as fast as you can for 10 seconds.
Then take a deep breath and relax. Repeat as necessary.
You may notice the images have a lesser effect on you as it's a bit like scrambling the image. It requires some concentration but 10 seconds isn't very long.
I don't generally have any porn images that bother me anymore as I haven't looked at porn all that much in the past month and a half (maybe once or twice?)
Hope this helps!