如果将图像插入（附加）帖子而不是外部链接：

function get_my_thumbnail($post_id, $size, $attr = \'\'){

  // check of featured image first
  $t = get_post_thumbnail_id($post_id);

  // no featured image set, check post attachments
  if(empty($t)){
    $attachments = get_children(array(
      \'post_parent\'    => $post_id,
      \'post_status\'    => \'inherit\',
      \'post_type\'      => \'attachment\',
      \'post_mime_type\' => \'image\',
      \'order\'          => \'ASC\',
      \'orderby\'        => \'menu_order ID\',
    ));
    $attachment = array_shift($attachments); // we only need one
    $t = $attachment ? $attachment->ID : false;
  } 

  // no attachments either...
  if(empty($t)) return \'no image...\';

  // we have either attachment / featured image, so output the post thumbnail
  do_action(\'begin_fetch_post_thumbnail_html\', $post_id, $t, $size); // compat
  $html = wp_get_attachment_image($t, $size, false, $attr);
  do_action(\'end_fetch_post_thumbnail_html\', $post_id, $t, $size);

  return $html;
}

功能如下：

function catch_that_image() {
global $post, $posts;
$first_img = \'\';
ob_start();
ob_end_clean();
$output = preg_match_all(\'/<img.+src=[\\\'"]([^\\\'"]+)[\\\'"].*>/i\', $post->post_content, $matches);
$first_img = $matches [1] [0];

// no image found display default image instead
if(empty($first_img)){
    $first_img = get_bloginfo(\'template_url\')."/images/no_image.gif";
}
return $first_img;
}

$imgURL = catch_that_image();