If you can use .htaccess files, create one with the code in it below, substitute domain.com with your domain.
RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(www\.)?domain.com/.*$ [NC]
RewriteRule \.(gif|jpg)$ - [F]
Place a copy in each folder where your images are placed.
Here is a good place where you can create different .htaccess files.
http://www.htaccesstools.com/