The problem with their web bug script is it requires the php-gd2 extension, it results in 95 byte output, and uses php gd code allocating memory... deallocating memory when its not necessary. This script when scaled up 100,000x has too large a footprint. It can be optimized into 3 lines as follows (with a 43 byte output):
<?php
//saves ip address and timestamp
file_put_contents("ip_list.txt", date("Y-m-d H:i:s") . ": ". $_SERVER['REMOTE_ADDR'] . "\n", FILE_APPEND);
header("content-type: image/gif");
//43byte 1x1 transparent pixel gif
echo base64_decode("R0lGODlhAQABAIAAAAAAAAAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==");
?>
