Si tienes acceso a la configuración del servidor web pues debuti, es cambiando una cosita:
Preventing People from Linking to Your Images
Add the following to the .htaccess file:
Rewrite Rule for images
RewriteCond %{HTTP_REFERER}<url of="" page="" accessing="" your="" domain="">
RewriteRule ^(.*)$ http://<same as="" above="" url="">
You would replace the <url of="" page="" accessing="" your="" domain="">above with the domain name and path of the page that is referring to your domain. For example: www.their-isp.net/users/mypage/
The RewriteCond directive states that if the {HTTP_REFERER} matches the URL that follows, then use the RewriteRule directive. The RewriteRule directive will redirect any reference back to the referring web page.</url></same></url>