Google Photos is a wrapper over Picasa Web Albums

Google Photos uses the Picasa Web Albums API, it doesn't have its own API:

• Google Plus API & photos? - Stack Overflow - use Picasa Web Album URL
• image - Google Plus Album Urls - Stack Overflow - all Google+ Photos are Picasa photos. You can get albums back as JSON too

No wonder my Picasa web albums showed up so well in Google Photos and why so many G+ features are missing -- Google chose to build on old Picasa rather than G+. It also explains why my old Mac Picasa uploader (works in Mavericks) is the best way to get images in albums to Google Photos.

The Google Drive integration, by the way, is a dangerous hack. Avoid it for now.

The Picasa uploader doesn't support Google Photo's image compression format (WebP?), so I wonder if those images will count against storage totals.

I hope we get an API, particularly with support for creating or selecting albums at upload time, any minute now...