[1] Google Photos APIs  |  Google Developers (2018-05-09 02:08:21 +09:00) https://developers.google.com/photos/

[2] Get started with REST  |  Google Photos APIs  |  Google Developers (2019-09-30 12:12:44 +09:00) https://developers.google.com/photos/library/guides/get-started

[3] Google Picker という API もあります。