[Plugin: FeedWordPress] How to use XPath-like syntax for Custom Post Settings?

Hello,
i want that every time FeedWordpress syndicate a post it capture the included image.

The RSS content is like this:

<?xml version="1.0" encoding="ISO-8859-1"?>
<rss version="2.0" xml:lang="en-US">
	<channel>
		<title>MySite</title>
		<link>http://www.mysite.com/index.php</link>
		<description><![CDATA[Live information from MySite]]></description>
		<item>
			<title><![CDATA[This is a test]]></title>
			<link>http://www.mysite.com/index.php/topic,13177.0.html</link>
			<description>
<![CDATA[<img src="http://s10.postimg.org/5zbyeuugp/testing2453.jpg" alt="" class="bbc_img" />

I'm testingTesting this right now]]>
			</description>
			<author>itsme@gmail.com</author>
			<comments>http://www.mysite.com/index.php?action=post;topic=13177.0</comments>
			<category><![CDATA[That section]]></category>
			<pubDate>Tue, 01 Oct 2013 22:26:56 GMT</pubDate>
			<guid>http://www.mysite.com/index.php/topic,13177.0.html</guid>
		</item>

How to catch <img src=”…”> string with XPath-like syntax?
How to fill the “Value” field?

This is the FeedWordpress feature i’m talking about:
http://img822.imageshack.us/img822/2333/5sw9.png