Web app's folder limitation

Question

Our web app stores all user images and videos in the file system.

We will have 10Million+ users. Which will eating a parent folder (in some share) which will have 10M sub folders (one for each user)

Do you know if windows will place any limitations on the number of subfolders the parent Images folder can have?

Is this a bad way to store users' file?

Note: it will be really bad, if someone tries to open the folder in win explorer :)

I have exposure to small no of users, but millions of users.

Please provide your valuable learning\experience.

Thanks for reading.