invalid XHTML link for CSS picture

Hello,

I just tried to validate
http://jigsaw.w3.org/css-validator/validator?uri=http://www.cof.ens.fr/video/ocean.css 

and I got this message:

<p>
 <a href="http://jigsaw.w3.org/css-validator/">
  <img style="border:0;width:88px;height:31px"
       src="http://jigsaw.w3.org/css-validator/images/vcss" 
       alt="Valid CSS!">
 </a>
</p>

Unfortunately, this isn't valid XHTML, because the <img> tag isn't
closed. I guess HTML accepts this, but XHTML doesn't. You should maybe
specify it, otherwise some people could insert invalid XHTML code in
their sheets wanting to use valid CSS...

Best regards,
Baptiste.