To stop hotlinking you can add the following to your .htaccess file. Replace example.com on line 3 with your own domain name. Also add or remove any file extensions on line 4
RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(www\.)example.com/.*$ [NC]
RewriteRule \.(gif|jpg|jpeg|png|bmp|zip|rar|mp3)$ - [F]
Maybe you prefer some mischief and want to serve alternate content when hotlinking is detected.
RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(www\.)example.com/.*$ [NC]
RewriteRule \.(gif|jpg)$ http://www.example.com/backside.gif [R,L]