in your .htaccess, put:
RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^
http://YOURDOMAIN.com [NC]
RewriteCond %{HTTP_REFERER} !^
http://www.YOURDOMAIN.com [NC]
RewriteRule .*\.([gG][iI][fF]|[jJ][pP][gG])$ - [F]
alternatively
RewriteEngine on
RewriteCond %{HTTP_REFERER} chatropolis.com [NC]
RewriteRule .* - [F]