Geoskeptic Photos is a private service run by Matthew Hanson for family members he invites.
What it stores about you: when you sign in with Google, the service receives your name and email address. They are kept in the sign-in system (Amazon Cognito) so you can stay signed in, and your email is checked against the invitation list on each request.
What it does not do: it does not read your Google account data, sell or share your information, or use it for advertising. Searches you run are not stored beyond ordinary short-term service logs.
Removal: ask Matthew to remove your invitation and account; access stops within a minute.
Contact: the person who invited you.