Interesting. Dan reports that Google is watching more closely than he expected.
I made an offhand comment on IRC with the URL for the real image (I hardlink it on the server, rather than playing Apache redirect games) and three minutes later... Pow! There was googlebot, looking at it. Turns out that one of the folks on the channel'd looked at it, and they run Opera with the google stuff on it so presumably that's how google got the URL. I will admit to being very impressed with the speed that the crawler struck out with (and it was the crawler, at least according to the log data and the PTR record for the IP address) but still...
Of course, it could have been the experimental IRC
sniffer bot they've been playing with.