This is what came up this afternoon on both the Focalplane main page badge as well as on Flickr itself. It appears to be a systemwide problem that Flickr is looking into. Some users have had porn substituted for their family friendly images. Not good. Perhaps Flickr needs to shut down the system until it's repaired?
(Update) Well, it was fixed within the hour - a bad cache server at Flickr HQ, apparently.