Users often use FTP or personal web servers to back up photos. If the "indexes" option is not disabled in the server’s .htaccess file, those backups become public.
To create this index, you can use metadata tags to label each JPG image with relevant keywords, such as: index of my boobs jpg
Replace generic names like IMG_1234.jpg with keyword-rich descriptions like navy-blue-velvet-blazer-mens-style.jpg . Users often use FTP or personal web servers