Are you looking for a way to require a featured image before you can publish a post? This snippet will require that you have added a featured image before your post can be published. If you try to publish a post without a featured image after adding this snippet, you will receive this message: “You must select Featured Image. Your Post is saved but it can not be published.”
Instructions:
All you have to do is add this code to your theme’s functions.php file or in a site-specific plugin:
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'><p><strong>You must select Featured Image. Your Post is saved but it can not be published.</strong></p></div>";
delete_transient( "has_post_thumbnail" );
}
}https://www.isitwp.com/require-featured-image-can-publish-post/