The reason why the image doesn't show is that flickr doesn't seem to allow hotlinking, i.e. showing the image directly on another page.
You are right. However:
Flickr ToS (excerpt):
"The Flickr service makes it possible to post images hosted on Flickr to outside websites. This use is accepted (and even encouraged!). However, pages on other websites which display images hosted on flickr.com must provide a link back to Flickr from each photo to its photo page on Flickr."
So, at first I hotlinked the image indeed but then I edited the post and inserted the html code snippet available on Flickr. I hope the image will reappear.