<script type="text/javascript">
var w = 1;
function machGroesser(e) {
  if(w == 1) {
    e.removeAttribute("width");
    w=0;
  } else {
    e.addAttribute("width");
    e.width={option};
    w=1;
  }
} 
</script>

<img border="0" src="{param}" width="{option}" onclick="machGroesser(this)">