clickable imagedata

In my XML document I have quite a few graphics like:

<figure>
  <title>Tux - der Pinguin</title>
    <imageobject role="html">
      <imagedata scale="50" fileref="bilder/master/sit3-shine-7.png"/>
    </imageobject>
  </mediaobject>
</figure>

The imageobject's get transformed to '<img src=...' and display the 
graphics in a scaled down version. That's OK.

How can I get links to the graphic files which show up in their full
size if the user clicks on them, like:
 <A HREF="bilder/master/sit3-shine-7.png">
  <IMG SRC="bilder/master/sit3-shine-7.png" width="270" alt="..." />
 </A>

Michael
-- 
                              http://www.miwie.org