Fix for the following Wordpress plugin: http://wordpress.org/plugins/wp-rss-images/

wp-rss-images.php

if($enclosure){ // this is Line 78
  list($width, $height, $type, $attr) = getimagesize($url);
	echo '<enclosure url="' . $image_url . '" length="' . $filesize . '" type="'.image_type_to_mime_type($type).'" />';				
}
if($media){
	list($width, $height, $type, $attr) = getimagesize($url);
	echo '<media:content url="'.$image_url.'" width="'.$width.'" height="'.$height.'" medium="image" type="'.image_type_to_mime_type($type).'" />';
}