Get image from RSS Feeds with no image URL

I would just like to to know how other developers manage to properly get/extract the first image in the blog main content of a site from URL in the RSS feed. This is the way I think of since the RSS feeds don't have image URL of the post/blog item in it. Though I keep on seeing

<img src="http://ift.tt/1oFDtqD" />

but it's only 1px image. Does this one has relevant value to the feed item or can I convert this to maybe the actual image? Here's the RSS http://ift.tt/1mWCPzw

Anyway, here's my attempt to extract the image using the url in the feeds:

function extact_first_image( $url ) {  
  $content = file_get_contents($url);

  // Narrow the html to get the main div with the blog content only.
  // source: http://ift.tt/1oFDqeu
  $PreMain = explode('<div id="main-content"', $content);
  $main = explode("</div>" , $PreMain[1] );

  // Regex that finds matches with img tags.
  $output = preg_match_all('/<img[^>]+src=[\'"]([^\'"]+)[\'"][^>]*>/i', $main[12], $matches);  

  // Return the img in html format.
  return $matches[0][0];  
}

$url = 'http://ift.tt/1mWCQ6I'; //Sample URL from the feed.
echo extact_first_image($url);

Obvious downside of this function: It properly explodes if <div id="main-content" is found in the html. When there's another xml to parse with another structure, there will be another explode for that as well. It's very much static.

I guess its worth mentioning also is regarding the load time. When I perform loop through out the items in the feed, its even more longer.

I hope I made clear of the points. Feel free to drop in any ideas that could help optimize the solution perhaps.