From the help--
What’s an Access Point? and what’s my Blog ID?
‘Access Point’, ‘Blog ID’, and ‘Platform’ are three absolutely vital pieces of information Photon uses to communicate with your blogging software. ‘Platform’ in itself is not a difficult question to answer; it should be quite well known to you whether you use Movable Type™ or TypePad™ to power your weblog, though the other two may pose some difficulty.
Movable Type users:
Your blog’s access point is the location of its XML-RPC server, found in your Movable Type installation directory with the name mt-xmlrpc.cgi. For example: http://www.example.com/mt/mt-xmlrpc.cgi
Your blog ID can be printed into any template using the template tag <$MTBlogID$>, and can alternately be found in the location bar of your browser while you’re logged in to Movable Type. For example: http://www.example.com/mt/mt.cgi?__mode=menu&blog_id=2
... does anyone know this for WordPress?