it trun out there is no proble with your server config,
it will prevent from guest visit these folders ,
forbidden /www.mysite.fr/htdocs/img/p/3/8/3/1/4/5
allow vist /www.mysite.fr/htdocs/img/p/3/8/3/1/4/5.xxx.jpg or other media files
usually this visitor is not normal ,he is a hacker maybe