another thing that works is authorizing specific people you KNOW are 18+ and setting the picture's "public viewers" setting to hidden. this works best if you want more control over who sees the pictures :^] 

i dont know how common this is but people who are under 18 can still set their birthday to be older than they actually are to see that kind of content and it's almost impossible to tell

i've seen someone do something like this where they asked for ID's and people who could provide em got authorization

i think tthe way it works is that anything w the sexual content tag (mild or explicit) is 100% hidden from users under 18. i believe that all users can see things mark only as nudity? but content filters can be changed in the settings (except that minors can't alter the sexual content filters obvisouly) DON'T quote me on this but i'm p sure th default is that nudity is hidden w a warning tag. buut i'm like 90% positive this is how it works. but i can confidently say that anything marked sexual is hidden to all minors

I think when images are marked with nudity or sexual themes *all* that content is blocked by users that have accounts with DOB under 18? But I don't know that 100%