Another reminder (because I’ve needed this many times) that you must enable WordPresses “Remote Publishing” protocols if you want to blog photos directly from Flickr  (a fantastic feature – I wish more people could do this but it remains a little tricky to set up both at Flickr and at WP unless you know this is needed (defaults have these boxes UNchecked).   I think you only need the XML-RPC after correct configuration at Flickr, but do both so you have more ways to publish to your WP blog:

Remote Publishing

To post to WordPress from a desktop blogging client or remote website that uses the Atom Publishing Protocol or one of the XML-RPC publishing interfaces you must enable them below.