Display different img src depending on hostname

I am trying to edit the logon.aspx file for Exchange 2010 OWA.
I have no knowledge on aspx coding, but some experience with VB, html, and php.

I'd like it to display 1 image for one domain, and a different image for another domain.

How can I achieve this?
Is there a way to set a string and use it later in aspx the aspx file?

Here is what I am trying...

<script type="text/javascript">
      if (location.hostname == 'mail.1.com')
      {
            lgntopl = "owa/14.1.438.0/themes/resources/lgntopl-1.gif";
      }
      if (location.hostname == 'mail.2.com')
      {
            lgntopl = "owa/14.1.438.0/themes/resources/lgntopl-2r.gif";
      }
</script>
<img src="<%lgntopl;%>" alt="">

When I load my page I get an error "XML Parsing Error: no element found"
So clearly, there is something wrong with my guessed logic above!

Any help, would be greatly appreciated.