# Example 1, block all hotlinking (when detectable)
location ~* (\.png)$ {
   valid_referers blocked mysite.com www.mysite.com;
   if ($invalid_referer) {
       return 405;
   }     
}    

# Example 2, redirect hotlinked files only for some sites
location ~* (\.mp4)$ {
   if ($http_referer ~ ^(http://www.bad.com|http://stupid.com) ) {
       # Redirect to a specific file
       #rewrite  ^/(.*)$ http://mysite.com/dont-hotlink.html last; 

       # Redirect to a dynamic url where /hotlinked/ is some script that
       # displays some info about the hotlinked file.
       rewrite  ^/(.*)$ http://mysite.com/hotlinked/$1/ last; 
   }   
}