[1] Google Photos APIs  |  Google Developers (5/8/2018, 5:08:21 PM) https://developers.google.com/photos/

[2] Get started with REST  |  Google Photos APIs  |  Google Developers (9/30/2019, 3:12:44 AM) https://developers.google.com/photos/library/guides/get-started

[3] Google Picker という API もあります。