Add Image to Image tags

// Add the image node to RSS feed
function add_rss_node_image() {
    global $post;
    if(has_post_thumbnail($post->ID)):
        $thumbnail = get_attachment_link(get_post_thumbnail_id($post->ID));
        echo "<image>{$thumbnail}</image>";
    endif;
}

add_action('rss2_item', 'add_rss_node_image');