Flickr deleted a controversial Barack Obama caricature; it nuked thousands of pictures over some comments about Obama. What sort of political expression is allowed on the Yahoo photo-sharing service? Unclear: Flickr decided a conversation on the topic was... not allowed.

After Flickr users asked on the site about the caricature, with some saying it was covered as transformative political speech, Flickr locked down the thread. That's hardly the first time; locking discussion threads about mysteriously deleted accounts is a routine occurrence at Flickr. It's a perplexing customer-relations move for a site that asks people to trust it with some of their most precious memories — and that faces intense competition from Facebook.

At least some discussions are allowed to run for a while before hey got locked, like this one, about a guy whose perfectly innocent account was mistakenly deleted.Flickr did eventually apologize to the guy and, unlike in most cases, was able to give him his digital photos back. Why? Because was deleting so many other people's pictures that it was backlogged and never got around to his. Progress!

(Pic: Taken at Twitter HQ by Daniel Catt.)