this gist is to improve wp featured image and set description

functions.php

<?php 
function new_post_thumbnail_meta_box() {
    global $post;
     echo '<p class="howto">Tamanho recomendado: 1413px × 640px </p>';
    $thumbnail_id = get_post_meta( $post->ID, '_thumbnail_id', true );
    echo _wp_post_thumbnail_html( $thumbnail_id );
     
}
function render_new_post_thumbnail_meta_box() {
    global $post_type;
     
    // Antigo metabox
    remove_meta_box( 'postimagediv','post','side' );
             
    // Novo
    add_meta_box('postimagediv', __('Imagem Destaque'), 'new_post_thumbnail_meta_box', $post_type, 'side', 'low');
}
add_action('do_meta_boxes', 'render_new_post_thumbnail_meta_box');