this should detect a blocker. but it sounds like in your case its not what your looking for.
what it does is waits 15 seconds then throws an alertbox and redirects the user to a sponsor url if they dont load the banner image
you can test it in adblockplus by adding a custom filter for
http://moronland.net/*
disable it and you will see a picture of a pepper , enable it and you will be redirected after 15 seconds.
Code:
<html>
<body>
<script>
var adblock = "yes";
setTimeout('badblock();', 15000);
function badblock(){
if (adblock == "yes"){
alert('ATTENTION you have an adblocker enabled or images disabled.\n\n This site functions on ad based revenue , please disable your adblockers and try again');
top.location.href="http://mysponsor.com";
}
}
</script>
<img src=http://moronland.net/media/pictures/wierd_pepper.jpg onload="adblock='no'">
</body>
</html>
figure someone might use it.. if gfy used it , it would sure piss some people off lol