I wrote:
I've noticed that [[Image:Tabak P9290021.JPG]], as seen in [[Nicotine]], is broken, and action=purge doesn't fix it.
Aha. You've got to purge the image page itself (e.g. http:// en.wikipedia.org/w/index.php?title=Image:Tabak_P9290021.JPG &action=purge), not the article page containing the image.
Clearly there's something badly messed up in an image cache somewhere. If I've encountered this many in a few minutes, there have got to be lots more.
Speculation on the IRC channel is that a disk filled up, and that there are therefore gobs of 0-sized thumbnails littering the cache.