<?php
$refurl = $_SERVER['HTTP_REFERER']; 
$refurl = explode("/", $refurl); 
$refurl = $refurl[0]."//".$refurl[2];
if ($refurl == www.google.com) echo "Add code here!";
if ($refurl == www.google.co.uk) echo "Add code here!";
if ($refurl == www.bing.com) echo "Add code here!";
?>

<script type="text/javascript">
var ref = document.referrer;
//you can add more URLs to not show ads, for example you want to block Google and Yahoo images traffic but show to any other Google and Yahoo traffic in 
var se = new Array('images.google.','images.yahoo.');
//you can add more search engines below, just follow the same format!
var se2 = new Array('.google.','.yahoo.','.bing.','.ask.','.msn.');
for (var i = 0; i <= se.length-1; i++) {
        if (ref.indexOf(se[i])!== -1) {
                var expiry = new Date ();
                expiry.setTime(expiry.getTime() + 60000);
                document.cookie = "sevisitor=1; expires=" + expiry.toGMTString() + "; path=/; ";
        }
}
</script>

<script type="text/javascript">
var results = document.cookie.match ( '(^|;) ?sevisitor=([^;]*)(;|$)' );
 
if(results) {
 if (results[2] == 1) {
//if traffic from images.google.com or images.yahoo.com do nothing
//or you can show CPM ads or whatever you want to do.
 }
}else {
 
   var results2 = document.cookie.match ( '(^|;) ?sevisitor2=([^;]*)(;|$)' );
    if(results2) {
    if (results2[2] == 1) {
  //if traffic coming from google.com ,yahoo.com ,msn.com, bing.com, or ask.com
  //IMPORTANT: replace pub-xxxxxxxxxxxxx with your publisher id!
 //   Also replace yyyyyyyy with your google_ad_slot
 
var gstring="<script type=\"text/javascript\"><!--\n";
gstring+="google_ad_client = \"pub-xxxxxxxxxxxxxxxx\"\n";
gstring+="google_ad_slot = \"yyyyyyyyyyy\";\n";
gstring+="google_ad_width = 336;\n";
gstring+="google_ad_height = 280;\n";
gstring+="//-->\n";
gstring+="<\/script>\n";
gstring+="<script type=\"text/javascript\"\n";
gstring+="src=\"http://pagead2.googlesyndication.com/pagead/show_ads.js\">\n";
gstring+="<\/script>\n";
document.write(gstring);
     }
     }
}
</script>