Are you using the Chrome browser? When someone copies an image that has already been uploaded to this forum, the URL associated with it starts with http, rather than https. The image won't show up using Chrome, at least not for me. You can however copy the address, edit in the "s", and view it in another window. Can't speak for other browsers.
I just checked. Same thing happened with Edge and IE-11. Could be there are some security settings that can be changed.