I saw some guy selling an anti hotlinking script for some $$$. But why pay.
Create a .htaccess file with this
Code:
RewriteEngine on
RewriteOptions inherit
RewriteCond %{HTTP_REFERER} !^http://([a-z0-9-]+\.)*yourdomain.com/ [NC] // yourdomain to allow hotlinkings
RewriteCond %{HTTP_COOKIE} !(^|(.+;)*)id=valid(;.*|$)
RewriteRule /*$ http://www.aftonbladet.com/ [L,R] //redirect hotlinkers to this url