La fonction getThumbnail permet la récupération rapide de l'URI de l'image à la une d'un article WordPress

hwlo_getThumbnail.php

<?php
/**
 * Return the thumbnail URI of an asked element
 * @param  int     $post_id  Article's ID, if necessary
 * @param  string  $size     Size of the thumbnail
 * @return string            Cover image URI
 */
function hwlo_getThumbnail($post_id = null, $size = 'thumbnail') {
    if (!is_numeric($post_id) && is_string($post_id)) {
        $size = $post_id;
        $post_id = null;
    }
    $thumb_id = get_post_thumbnail_id($post_id);
    $thumb_url = wp_get_attachment_image_src($thumb_id, $size);
    return $thumb_url[0];
}