How to add a thumbnail to your WordPress RSS feed

To make sure your RSS feed stands out in the crowd you can make it look a little bit nicer by adding a thumbnail to it. The following code should be placed in functions.php and it adds a thumbnail to both to the full RSS feed and also to the excerpt version if you choose to use that one.

function rss_post_thumbnail($content) {
	global $post;
	if(has_post_thumbnail($post->ID)) {
		if (get_option('rss_use_excerpt')){
			$content = '<p>'.get_the_post_thumbnail($post->ID).'</p>'.get_the_excerpt();
		}else{
			$content = '<p>'.get_the_post_thumbnail($post->ID).'</p>'.get_the_content();
		}
	}
	return $content;
}

add_filter('the_excerpt_rss', 'rss_post_thumbnail');
add_filter('the_content_feed', 'rss_post_thumbnail');