Need a little help

I'm trying to redirect based on referring host and request. I have an .htaccess set up like this: RedirectMatch (.*)\.gif$ http://www.domain.com/_borders/test.php to redirect all requests for .gif's to a php script which then determines the referring host. $url=parse_url($HTTP_REFERER); if ($url[host] == "domain.com") { //this is where I get stuck do something } else {do some thing} how to I return the correct image. I.e. if the referring page has an <img src="mydomain.com/image"> link and I redirect requests for that image to the php script to determine the host how can I now return a different image for display into the page. Make sense? Is it possible? -Brian