Question

My question is not like this one: Browser-independent way to detect when image has been loaded

I have advertisements on my site for which I get paid per impression, now recently I have seen a dramatic drop in the number of impressions that each ad has been getting however I have been getting more average hits/month. Is it possible for me to detect if an image has been loaded or if something like a 404 (common with cheap ad blockers) has been loaded instead?

Answer 1

How are you counting now? Judging by your question I suspect you’re parsing the server log or the images are served via a dynamic url. If this is the case then the drop could be caused by client or proxy caching. Users are viewing the ads but the request never hits your server.

The obvious solution would be to disable caching but this is extremely rude to your visitors. The common approach now is to use a 1px GIF as a beacon to count an ad. JS would work too but you lose hits when JS is disabled.

<div id="ad">
  <img src="/real.gif?ad_id=3435">
  <img src="/beacon.php?ad_id=3435&random=6354377">
</div>

BTW: If the counting is done by the ad provider then there’s always the possibility they are lying. Marketting people aren’t generally the most honest or principled of folk.