It looks like the host used for Add image to post postimgage.org have changed their TOS no longer allowing "adult imagery" but their own Mod page still mentions the option but the dropbox is no longer there. So I'm guessing the TOS is correct.
I now checked the more recent pictures that are still up use postimg.cc instead of postimg.org so links are just broken changing from .org to .cc brings the images back on some that I've tried. Otherwise the gallery, attachments in posts or linking back to images original source may be more of guarantee the images will stick around.
At first I thought images may of been deleted but this seems to be wrong