Login Authentication Via Google+, Twitter, etc.
I'm unable to find this in the documentation so I am suggesting additional login choices (google+, twitter, linkedin, yahoo, etc.) for visitors.
Another candidate, http://accountchooser.net/owners from the OpenID Foundation.
I just requested this in the Github though a little different.
A visitor does not necessarily want to create a new gallery for themselves if they were just invited to view an album.
This would be even better than my suggestion which was to just make it an option at registration to create a gallery or just be a visitor.
The next question could be: how do you select those users so that you can share photo's with them?
Right now you can create groups with e-mail adresses, but that seems limited.
Google Apps domain authentication / single Sign in would be great.
Olivier Berger commented
WebID, OpenID, etc.