...it will cause an event to generate a particular piece of code...

That's a little vague but this might be enough to get you started. It's JS but the use of Perl often involves sidebars like JS and SQL.

<script type="text/javascript">
function postToApp () {
  alert('Generating code... Or opening a CGI with args... or...')
  return false
}

document.write('<img src="" style="border:1px solid ')
document.write('black;width:80px;height:100px;" ')
document.write('onclick="postToApp()" ')
document.write('alt="no source!" />')
</script>
<noscript>
Special functions are reserved for those less paranoid. Enable
JavaScript in your browser to use this.
</noscript>
[download]

The Rhino and The Howler Monkey are both good investments, of course.