Developer site: https://developers.google.com/photos

With the API you can help users transfer, share and bring their content into your app more easily (including features like auto-organized categories and creating link-shareable albums).

API is now launched to General Availability, with official client libraries and sample apps for Java & PHP (and more in the works!).

Large app integrations are also encouraged to join the Google Photos Partner Program. Check the developer site for more info.