I use a very simple version and just stick it in my image directory:
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RewriteEngine On
RewriteCond %{HTTP_REFERER} !^http://www.yourdomain.com.* [NC]
RewriteCond %{HTTP_REFERER} !^http://yourdomain.com.* [NC]
RewriteCond %{HTTP_REFERER} !^http://www.yourdomain.com:80.* [NC]
RewriteCond %{HTTP_REFERER} !^http://yourdomain.com:80.* [NC]
RewriteRule /*
http://www.where_you_want_to_redirect.com [R,L]
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You can use the last line to redirect surfers that try browsing your image directory. You can save the above as a .txt file and then upload it to your image directory. Once you upload it, rename the file to .htaccess