[ISAPI_Rewrite]
RewriteCond Host: (.+)
RewriteCond Referer: (?!http://\1.*).*
RewriteCond Referer: (?!http://(?:.*\.google\.com|google\.com|.*\.baidu\.com)|baidu\.com).+
RewriteRule .*\.(?:gif|jpg|jpeg|png|bmp|exe|rar|zip|mp3|wma|avi) /block.gif [I,O,N]