Put featured image under post title in admin area

Question

Instead of inserting a new column with a featured image on it, I would like to put the featured image under the post's already existing title. I can't seem to figure out how you insert things on the title property however. Achieving this:

I've found this post: How can i place Feature Image under title field in wp-admin?

With a snippet that I can't get to work. Otherwise there are lots of solutions for adding new columns with featured images in them.

I've arrived at something like this:

add_action('admin_head-edit.php', function(){
    add_filter('the_title', function( $title, $id ) {
        return $title . get_the_post_thumbnail_url();
    }, 100, 2);
});

But if I use get_the_post_thumbnail_url the url is embedded as part of the title, and if I use the_post_thumbnail( 'thumbnail' ) it renders the image twice.

Answer 1

add_action('admin_head-edit.php', function(){
    add_filter('the_title', function( $title, $id ) {
        return $title . the_post_thumbnail( 'thumbnail' );
    }, 100, 2);
});

Will produce 2 images because there are two titles on custom posts, apparently. One that is hidden and one that isn't. Adding the image markup to the hidden element will break the CSS that hides it. So the solution is to insert admin-css that hides it.

    .column-title .hidden ~ img{
        display: none;
    }