WP Require Featured Image on Post

featured_image.php

<?php
# Taken from: http://www.wpkube.com/code-snippets-wordpress/

add_action('save_post', 'wpds_check_thumbnail');
add_action('admin_notices', 'wpds_thumbnail_error');

function wpds_check_thumbnail($post_id) {

// change to any custom post type
if(get_post_type($post_id) != 'post')
return;

if ( !has_post_thumbnail( $post_id ) ) {
// set a transient to show the users an admin message
set_transient( "has_post_thumbnail", "no" );
// unhook this function so it doesn't loop infinitely
remove_action('save_post', 'wpds_check_thumbnail');
// update the post set it to draft
wp_update_post(array('ID' => $post_id, 'post_status' => 'draft'));

add_action('save_post', 'wpds_check_thumbnail');
} else {
delete_transient( "has_post_thumbnail" );
}
}

function wpds_thumbnail_error()
{
// check if the transient is set, and display the error message
if ( get_transient( "has_post_thumbnail" ) == "no" ) {
echo "
<div id="message" class="error">

You must select Featured Image. Your Post is saved but it can not be published.

</div>
";
delete_transient( "has_post_thumbnail" );
}

}