I use pluckeye. It's free and it work by blocking all images and videos on the web. You can choose to allow certain websites and even set specific times to allow certain websites (for example I have youtube allowed only at certain times of day). It works with a delay you set, so any changes you make take however long you set your delay to come into effect (mine is two hours). Inconvenient? Yes. So is porn addiction. But it is also super effective if used correctly.