Javascript will do exactly what you want. The only caveats are that it only measures ppl with js enabled, and browser bugs cause a decent # of false referrers (meaning the 'referrer' may actually be the site they were at before they typed in your url, etc).

<SCRIPT LANGUAGE="JavaScript">
<!--//
var lt = unescape("%3c");
var gt = unescape("%3e");
var qt = unescape("%22");
var sq = unescape("%27");
document.write(lt + "IMG SRC=" + qt + "http://www.phu.bar/cgi-bin/");
document.write("count.pl?referrer=");
document.write(escape(document.referrer));
document.writeln(+ qt + gt);
//-->
</SCRIPT>
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