我遵循这种方法getting images from the media library.

// get the first image attached to the current post
function aldenta_get_post_image($size = \'thumbnail\') {
    global $post;

    $photos = get_children( array(\'post_parent\' => $post->ID, \'post_status\' => \'inherit\', \'post_type\' => \'attachment\', \'post_mime_type\' => \'image\', \'order\' => \'ASC\', \'orderby\' => \'menu_order ID\') );

    if ($photos) {
        $photo = array_shift($photos);
        return wp_get_attachment_image($photo->ID, $size);
    }

    return false;
}