check the presence of a Face before sending

[dgiglio@iol.it (daniele.g (alias giglio robbo' d'acciaio))]

I use 

(add-hook 'message-send-hook 'random-face-header-insert)

to insert a Face header before sending my posts.

But this function doesn't check if such header is already present among
others.

This is my code:

--8<---------------cut here---------------start------------->8---
(defun random-face-header-insert ()
  (let* ((faces (directory-files "~/News/xfaces" t "\\.png\\(\\.0\\)?$"))
	 (face (nth (random (length faces)) faces)))
    (save-excursion  
      (goto-char (point-min))    
      (insert "Face: "  (gnus-convert-png-to-face face) "\n")    
      (when (string-match "0$" face)
	(insert "Face: "
		(gnus-convert-png-to-face (replace-match face "0$" "1"))
		"\n")))))
--8<---------------cut here---------------end--------------->8---

How can I improve it?
-- 
 La prima prova di buon senso e' nel non pretendere di risolvere tutto
 col buon senso.
 		-- Ugo Bernasconi