Add image to RSS feed

gistfile1.php

/**
 * Add namespace for the featured image to RSS feed
 *
 * @return string
 */
function rss_img_adding_yahoo_media_tag(){
	echo 'xmlns:media="http://search.yahoo.com/mrss/"';
}
add_action( 'rss_ns', 'rss_img_adding_yahoo_media_tag' );
add_action( 'rss2_ns', 'rss_img_adding_yahoo_media_tag' );

/**
 * Add featured image to RSS feed
 *
 * @return string
 */
function rss_img_include() {
	global $post;

	if ( $thumbnail_id = get_post_thumbnail_id( $post->ID ) ) {

		$img = wp_get_attachment_image_src( $thumbnail_id, 'full' );

		if ( !empty( $img ) ) {

			$url = parse_url( $img[0] );
			$path = ABSPATH . ltrim( $url['path'], '/' );

			if ( file_exists( $path ) ) {
				echo '<media:content url="' . esc_url( $img[0] ) . '" width="' . esc_attr( $img[1] ) . '" height="' . esc_attr( $img[2] ) . '" medium="image" type="'. esc_attr( get_post_mime_type( $thumbnail_id ) ) . '" />';
			}
		}
	}
}
add_action( 'rss_item', 'rss_img_include' );
add_action( 'rss2_item', 'rss_img_include' );