When you use a blogging client from your computer/mobile-phone to upload photos to WordPress, WordPress resizes the 
image into smaller versions (e.g. thumbnail and medium) but the URLs of these resized images aren’t returned to 
the client so it can’t use them.
If clients are altered to support this plugin, when you include photos in an entry, the entry could automagically 
include the smaller images which link to the full size version when clicked on.
There is a patch to add the functionality in this plugin into the core of WordPress: 
https://core.trac.wordpress.org/ticket/6430 
but it missed the cut-off from WordPress 3.0 so it is unlikely to to be included for some time to come.

ImageURLReturner

When an XML-RPC Wordpress client uploads a photo, this plugin add the URLs for the resized images to the response so they can be used by the client in …

Max Cutler

This plugin brings XML-RPC API enhancements from the WordPress 3.4 release to previous versions 
of WordPress (3.3 and earlier). It also adds new user management methods.
It is derived from Prasath Nadarajah’s GSoC ’11 project to expand WordPress’ web services, 
although the exposed API methods are not compatible (different parameter names/types/orders).
<h4>Methods</h4>
New Methods:
<ul>
<li>wp.newUser – create a new user</li>
<li>wp.editUser – edit user information</li>
<li>wp.deleteUser – delete a specfic user</li>
</ul>
3.5 Methods for pre-3.5 sites:
<ul>
<li>wp.getUser – get information about a specific user</li>
<li>wp.getUsers – retrieve a list of users</li>
<li>wp.getProfile – retrieve information about the requesting user</li>
<li>wp.editProfile – edit the profile of the requesting user</li>
<li>wp.getRevisions – retrieve revisions for a specific post</li>
<li>wp.restoreRevision – restore a post revision</li>
</ul>
3.4 Methods for pre-3.4 sites:
<ul>
<li>wp.newPost – create a new post (of any post type)</li>
<li>wp.editPost – edit a post (of any post type)</li>
<li>wp.deletePost – delete a post (of any post type)</li>
<li>wp.getPost – get a specific post (of any post type)</li>
<li>wp.getPosts – get a list of posts</li>
<li>wp.getPostType – get information about a specific post type</li>
<li>wp.getPostTypes – get a list of registered post types</li>
<li>wp.getTaxonomy – get information about a specific taxonomy</li>
<li>wp.getTaxonomies – get a list of registered taxonomies</li>
<li>wp.newTerm – create a new term in a taxonomy</li>
<li>wp.editTerm – edit a term in a taxonomy</li>
<li>wp.deleteTerm – delete a term in a taxonomy</li>
<li>wp.getTerm – get information about a specific term in a taxonomy</li>
<li>wp.getTerms – get a list of term associated with a taxonomy</li>
</ul>

XML-RPC Modernization

excelent

This plugin updates the WordPress XML-RPC API to leverage the latest features of WordPress and move beyond the historical Blogger/metaWeblog/MT APIs.

ImageURLReturner vs XML-RPC Modernization