The author of an album or document can invite for viewing via the built-in e-mail message service. The moment an email is sent, a new user record is created with the specified email address. In this case, the invited user also has access to the album or document.
If the user invited via email has own Photo Pick account, this album will also appear in the account. The invited user can delete this album, but the album will not be deleted from the author's account.
The invited user can view the album and select images, but cannot delete the album or images. Also doesn't have edit access.
This is represented, for example, in the author's account:
This is how it appears in the invitee's account: