There are two options to see how many people logged into your Photo Website. First go to your GoPhoto - CMS and login with your credentials.
Dashboard
On your dashboard you find 'Visitors statistics'. Here you can see how many people logged into your Photo Website that day.
Statistics - Visitors
When you want to see an overview of how many people logged into your Photo Website over a different period of time go to 'Statistics' - 'System' in the sidebar.
Here you can change the date and get an overview over a different period of time. You can view these statistics daily, weekly, monthly or yearly.