I've recently started using qustodio. The free version is still a pretty good blocker . (You can pay to get a bunch more features)
Another approach is Pluckeye. It's a bit more radical though. It blocks all pictures and videos on all websites by default. However, Pluckeye is very customizable. You can black- and whitelist specific sites you use often. Pluckeye also isn't using a password protection system, but rather a delay cycle system. It was specificly designed for self-administrating addicts. It works like this: You set a specific time as delay (e.g. 2 hours). Every change you make to the rules (e.g. allowing a website), will only take effect after the cycle has run out (i.e. after 2 hours in this case). This allows you to buy yourself more time before doing something stupid.