If you originally viewed the images in Safari before linking them, you may have "authorization" from the site via direct viewing rather than offsite linking/referencing and thus they may either simply load, or be present in your cache. If I first copy the image URL then paste it in the address bar and load (which does show the image), then go back to this thread, it does show the image I viewed separately in-line in the post. But the other image I haven't done that with yet does not show. So it's something to do with remote linking of images on that particular site, a practice which is often frowned upon so it's not really surprising it doesn't work. I'd suggest simply linking to them rather than embedding.
- Oshyan