We should remove that checkbox since it is a hack and doesn’t work now. Even the nsfw system is a hack I wish discourse forum software had something inbuilt for such things. Also deciding what is nsfw and what is not is really bothersome.
Please ignore the checkbox it doesn’t work and I will remove that all nfsw image will be blurred.
Meanwhile with all the hassle I think it is better to state on the signup that the website contains nsfw images and if you are under age using the forum should need parental supervision or better we should close the forum for under 18 people and be done with this nsfw shenanigans 
(sorry for the rant. And please take it with a pinch of salt. I am just stressed with the moderating the posts that need me to write a rule book with extreme detail of what constitutes a nsfw and what not)