Put all your images in an folder. Then put this htaccess in the images folder.
Code:
ErrorDocument 403 http://www.sexae.com/403.html
RewriteEngine On
RewriteCond %{HTTP_REFERER} !^http://([a-z0-9-]+.)*sexae\.com/ [NC]
RewriteRule .* - [F,L]
That is mine... replace it with your own domain.