My school uses Webroot for its proxy (which doesn't block Imgur, but semi-blocks the forums) and the DNS is OpenDNS which does block Imgur, but not the forum (or new websites)
It's really simple to get past the DNS block on mobile, just use a different one.
For computers, I just do the best of both worlds and have the BLF ignore the proxy.
edit: blockland.us is completely blocked on both though