Hey.
I have the same need to add a thumbnail to my rss feed. If I check my own feed I just see a post image and not the thumbnail. Unfortunately if I just include a youtube video and no image in the post but set a thumbnail there is no image at all.
My WP Version is 3.5.1
I already added this piece of code to my functions.php:
function rss_post_thumbnail($content) {
global $post;
if(has_post_thumbnail($post->ID)) {
$content = '<p>' . get_the_post_thumbnail($post->ID) .
'</p>' . get_the_content();
}
return $content;
}
add_filter('the_excerpt_rss', 'rss_post_thumbnail');
add_filter('the_content_feed', 'rss_post_thumbnail');
But that didn’t change anything.