Chastity/orgasm denial is a fun one, but there’s very few pictures of it - only 134 images tagged “chastity” on Derpibooru, in fact.
Long term chastity is especially interesting to me - where someone is forced to wear a chastity cage or belt for up to weeks at a time, not necessarily knowing when they’ll be allowed their next orgasm, and potentially being teased frequently and left in a state of constant frustration by their keyholder.
Unfortunately, there’s even fewer long term chastity pics on this site - most of them seem to be short term/play chastity, where someone is wearing a chastity device for the duration of a bondage/play session, and would (presumably) have it removed once that’s over. It kinda makes sense though - it’d be pretty difficult for a pony to wear a chastity device (especially a belt) for weeks at a time without anyone noticing it.