num_images = 21;

function randomScreenshot() 
{
    index = 1 + Math.floor(Math.random() * num_images); 
    
    document.write('<a href="http://www.darwinia.co.uk/about/screenshots.html">');
    document.write('<img border="0" vspace="0" hspace="0" src="http://www.darwinia.co.uk/screenshots/t_image' + index + '.jpg">');
    document.write('</a></td>');    
}