You can see it because you have visited the TGN site and so the image is already in your temporary internet cache thingy. Your browser is intelligent enough to look for it there. People who haven't been there don't see it because the TGN site probably blocks hotlinking (or something, hell I dunno, I'm not a scientist, but with these hotlinking issues the person who posts it can usually see the thing, but nobody else can. That's why it's a good idea not to hotlink to other people's pictures. You never quite know when you are making yourself look like an ignorant fool who can't operate a computer).