There are many pictures that I have posted to the photos site that are not visible to the general public.
If I know you, you can sign up for an account, then Email me your login name. I will then enable your account to see the rest of the photo collections. This includes categories like, “Friends at Work” and “Friends at Hotel”.
If I don’t know you, you can still sign up for an account, but you’ll get no benefit, and will have given your Email address to another random site on the internet. Why would you do that?