prima immagine nel post come thumb

<?php
$attachments = get_children(array
('post_parent' => get_the_ID(),
 'post_type' => 'attachment',
 'post_mime_type' => 'image',
 'orderby' => 'menu_order'));
if ( has_post_thumbnail() ) {
the_post_thumbnail( array(150,150) );
} elseif ($attachments) {
    if ( ! is_array($attachments) ) continue;
    $count = count($attachments);
    $first_attachment = array_shift($attachments);
    echo wp_get_attachment_image($first_attachment->ID);
} else {
    echo '<img src="' . get_bloginfo( 'stylesheet_directory' ) . '/images/default.jpg" />';
}
?>