Before you proceed, the most important piece of information you need to know is that while Serendipity uses BloggerAPI (or the MoveableType extension to BloggerAPI), Flick'r DOES NOT work properly with that setting. (You will ended up with a Draft post devoid of a Title waiting for you to "publish" it officially -- need to login as admin before you can see that). That's not good.
Instead, you must choose the "MetaWeblogAPI Enabled Blog" setting (just like WordPress'ers would). The API Endpoint (or Webservice path) for Serendipity is http://path.to/serendipity/serendipity_xmlrpc.php. Put in your Flick'r ID/PW and you are good to go.
"This is a test post from
, a fancy photo sharing thing."Oh, when you "blog" your photo from Flickr, you will get a message that say it has fail to post and your blog software is "flakey". But if you check your blog, you will find the photoblog posted and well. So enjoy!