Find the .htaccess file in your root installation directory or inside the private images folder. If it doesn't exist, create a blank text file and name it .htaccess .

If you're looking for something specific like a software or a service to manage private images, more context (like operating system, specific software requirements, etc.) would be helpful.

Try visiting ://yourdomain.com in an incognito window to verify it triggers a 403 Forbidden error.

Preventing exposed installations and securing your private assets requires proper web server configuration and structured file management. Why Directory Browsing Happens

When a user requests a URL that points to a directory rather than a specific file, the web server looks for a default index file to display. If that file is missing, the server makes a choice: display a 403 Forbidden error, or generate a list of the directory's contents.

How do I disable directory browsing? - apache - Stack Overflow