Here's a weird one for you. When I'm logged in, I cannot see my own pictures. Everyone else's pictures show up fine though. Logged in: Not Logged In:
I remember some others posts in which the image was not shown, logged or not (I hope the owner saw them, and thus didn't complain something was wrong). Trying to load the image alone gave "access denied". My guess is some accounts are misbehaving, because there doesn't seem any place to handle permissions.
same for me, there are some picture i can't see while other have commented on them so it must be working for other members.
Yesterday your images worked, but not today. It seems to be spreading https://forum.corvusbelli.com/threads/thumbnail-pictures.9257/
