Who can view and access a gallery?
In principle, anyone to whom you give the direct address of a gallery can also access it.
So you alone are responsible for who can see your galleries.
Therefore, we always recommend two things:
Protect your galleries with a password, especially when it comes to sensitive topics. (weddings, erotic pictures, company secrets etc.)
Always use secure links and deactivate the clear link of a gallery if necessary. (What exactly is a "secure link"?)