避免伺服器上的檔案直接被網址存取

RewriteEngine on 
RewriteCond %{HTTP_REFERER} !^http://(www\.)?domain [NC] 
RewriteCond %{HTTP_REFERER} !^http://(www\.)?domain.*$ [NC] 
RewriteRule \.(jpg|jpeg|png|gif)$ - [F]

[NC][F] flags 使用請參考
https://httpd.apache.org/docs/2.4/rewrite/flags.html