それをphpでやる場合は
JSでhoge.phpに

JS側
if (document.referrer == parent.frames.location) {
refer = top.document.referrer;
} else { refer = document.referrer; }
refer = escape(refer);
document.write('<img src="hoge.php?referer=' + refer +'">');

php側
<?php
$ret = null;
if (isset($_GET['referer'])) {
 $ref = $_GET['referer'];
}

ここらへんで$ref似格納してあるリファラの処理

// 以下画像出力
$img = "R0lGODlhAQABAIAAAP///////yH5BAAHAP8ALAAAAAABAAEAAAICRAEAOw==";
header("Content-Type: image/gif");
echo base64_decode($img);