what do you want exactly and dose it have to be in PHP because i think i can do it in a .htaccess file?
I can make one so they have to have visited your main site within that session to get the files will this do? This will require .htaccess PHP
Top of homepage <?php session_start(); $_SESSION['in'] = true; ?> PHP: Top of image returner: <?php session_start(); if($_SESSION['in'] !== true) die(header('Location: index.php')); ?> PHP: