Originally Posted by OldCoot
Can you see this one?
Yes, because it's a forum attachment (i.e. uploaded to this server vs. coming from the sticker maker's site).
Unfortunately, it's not a good test because I can now see both of them.
I'm 99.5% positive it has to do with me visiting the sticker site. I'm betting it set a cookie on my machine to say that I'd visited there and am now "allowed" to see direct image links.