This script just set the following headers:

Set-Cookie: foo=bar; path=/
Content-Type: text/html

Blue images means the cookie was sent during the image request. Red images means the cookie was not sent.

Requesting cookie-based image from www.xav.com:

http://www.xav.com/images/xs_cookie.pl?image

Requesting cookie-based image from www.nickname.net:

http://www.nickname.net/images/xs_cookie.pl?image