How is this redirect done?

If you look at the code below and click on the first link, which looks like an image url, It redirects to another page.

How are they doing this?

 <td height="326"><a target="_blank" href="" rel="nofollow">
            <img src="" width="640" height="480" border="1">

They are probably using server side scripting to redirect the page but it looks rather dodgy to me.

Ugh, dodgy is an understatement.