use htaccess to prevent hotlinked images

RewriteEngine on

RewriteCond %{HTTP_REFERER} !^http://yoursite.com/.*$ [NC]
RewriteCond %{HTTP_REFERER} !^http://yoursite.com$ [NC]
RewriteCond %{HTTP_REFERER} !^http://www.yoursite.com/.*$ [NC]
RewriteCond %{HTTP_REFERER} !^http://www.yoursite.com$ [NC]
RewriteRule .*\.(jpg|jpeg|gif|png|bmp|js|css)$ – [F,NC]