I'll look into what's happening, but in general it's expensive / complicated to delete from edge-caching CDNs.
If there is a photo that gets constant traffic, the edge caches will do their job of keeping it around. Poking around the Googles, it looks like this URL has been reposted a lot, which creates a self-fulfilling prophecy and will keep it around in cache.
http://www.google.com/search?q=5013_96426961157_709851157_21...