In the beginning there was Picasa
Picasa Web Albums which is still available today comes with a fully-fledged API with read & write access to fully manipulate and organize photos. Admittedly the old GData APIs aren't the nicest to work with compared to modern APIs, especially for client-side applications in JS, but the API still does its job today.Probably the most useful API calls for read-access, since the documentation can be a bit confusing:
Request a list of albums:
https://picasaweb.google.com/data/feed/api/user/{{userid}}Info about one album:
https://picasaweb.google.com/data/entry/api/user/{{userid}}/albumid/{{albumid}}List photos in an album:
https://picasaweb.google.com/data/feed/api/user/{{userid}}/albumid/{{albumid}}Along came Buzz
Here's a blog post for those who still remember the good old times:http://googlephotos.blogspot.co.at/2010/02/photos-in-google-buzz.html
Google Buzz didn't really change much about how Picasa Web Albums and the associated API worked, it mostly seemed like Buzz was using the API itself to achieve all the features.
One feature that was introduced was the concept of "Photos from Posts" that automatically created special albums in Picasa for each post with photos you shared to Buzz. Those albums could be recognized in the Picasa Web Albums API with the
<gphoto:albumType>Buzz</gphoto:albumType> tag they had assigned in the album description.Funny enough photos shared directly in posts on Google+ today still generate "Buzz"-albums.
On the plus side...
With Google+ we got a new UI for managing photos that in many ways still is more cumbersome to use than the old Picasa Web Albums UI. But the album and photo IDs matched so it was easy to use the Picasa Web Albums API for programmatic managing of your Google+ photoshttps://plus.google.com/.../6155360510478436241/6155360509668083954
https://picasaweb.google.com/data/.../6155360510478436241/.../6155360509668083954
https://picasaweb.google.com/...#6155360509668083954
With Google+ the new concept of sharing albums to circles was introduced. Those albums would show up with
<gphoto:access>private</gphoto:access> and you could (and still can) retrieve the information about what people and circles albums were shared with by requesting the acl of an album:https://picasaweb.google.com/data/feed/api/user/{{userid}}/albumid/{{albumid}}/acl
This would show information like this:
<entry> <gAcl:scope type='group' value='...'/> <gphoto:nickname>Photo Share Test</gphoto:nickname> </entry> <entry> <gAcl:scope type='user' value='...'/> <gphoto:user>116...</gphoto:user> <gphoto:nickname>Scarygami Test</gphoto:nickname> </entry>
Google+ also introduced Instant Upload (or Auto Backup as it is called) creating a new automatic album with the
<gphoto:albumType>InstantUpload</gphoto:albumType> tag. As with "buzz" the "InstantUpload" name stayed in the API even after the name was changed in the front endAt the Drive-In
Things started to get a little bit weird with Google Drive integration.It began with the feature to show (some but not all) photos stored on Google Drive in the Google+ Photos UI, with each Drive Folder that contained photos getting their own album.
Those albums wouldn't show up when requesting the list of albums from the Picasa API, but you could request some information and the photos inside if you copied the album ID from the corresponding Google+ URL (https://plus.google.com/photos/.../albums/{{albumId}})
Things got even more confusing when Google(+) Photos were added to Google Drive. This allowed you to add a folder to your Drive which would include all the photos you uploaded and shared on Google+ sorted by year and month. You can then go ahead and re-arrange/edit the photos as you want, but... the sync is one-way and one-time only, meaning that changes done on Google Drive won't be reflected back to Google Photos and you only get the originally uploaded photo in Google Drive without any changes that you might make in Google Photos at a later point.
You can access those photos using the Drive API using the
files.get and files.list methods, and you also have write access using insert/update/patch methods, and the Drive API being one of the newer discovery-based APIs is much nicer to work with than the antiquated Picasa API. But it won't help you in managing your Google+ Photos since the data isn't synced, and there is no indication whatsoever in the file meta-information that the files originally came from Google+. The photos in Google Drive also have completely different IDs than the ones you could use in the Picasa API, they are completely decoupled.New and shiny?
And so we reach the present with the new Google Photos UI to replace the Google+ Photos UI.Since there are several essential features missing, like the possibility to add geotags, I've been thinking about creating some extensions/scripts to do some of the things via the Picasa API. The problem is that Google Photos invented completely new IDs for photos and album that don't match the corresponding IDs in the Picasa API, even though the photos and albums still show up there.
The Picasa IDs show up nowhere in the page source so they could be parsed, and the Google Photos IDs don't show up anywhere in the Picasa API which makes finding a matching photo to work with in the Picasa API nearly impossible. You could parse some meta information (like date/filename) from the Google Photos page and try to find a match in the Picasa API but that is (a) bound to break regularly as the Google Photos page gets updated and (b) potentially requires a lot of API requests until you get where you want. But that seems to be the only possibility at the moment to get some programmatic access to your photos, or you could completely forget about Google Photos and continue using Picasa Web Albums and the API to manage your photos, only using Google Photos for uploading/backing up/editing/sharing photos.
Talking about sharing: with Google Photos the main way of sharing albums is to create a "secret link" that can be shared and viewed by anyone who has the link. That also means that all albums created with Google Photos now will always show up with
<gphoto:access>private</gphoto:access>.Sharing to Google+ still allows you to share to circles/people without creating the shareable link, and those access permissions are still visible in the Picasa API.
The Picasa API gets a little bit confused though when sharing publicly to Google+. Those albums show up as private in the API, and are shown as "Limited, anyone with the link" in the Picasa Web Albums UI. To make things a little bit more confusing those publicly shared private albums show up in the API even when not authenticated as the owner of the album:
Example of a public private album in the API
A New Hope
It's been almost 4 years now since a blog post about a potential Google+ Photos API was leaked.While being read-only (as most of the Google+ API) this seemed like a promising start to replace the antiquated Picasa Web Albums Data API. But nothing ever happened there anymore and with Google Photos now getting decoupled from Google+ the Plus API doesn't seem to be right place to add such an API.
As discussed above the Google Drive API probably won't be a good home for new photos features either since there is no sync happening after the initial upload, even though it would be possible to represent most metadata related to albums/sharing/editing using custom file properties.
So it seems that we still have to wait for a separate photos API and try to use the Picasa Web Albums UI now as long as it is still working. The minimal functionality I would wish for is a way to map Google Photos IDs to Picasa IDs...
For lack of a better place you might want to star this feature request and maybe add a comment about what you would want to do with a Photos API and what features you are expecting to see in such an API.
Alternatively/additionally you can also use the feedback option in the new Google Photos site/app to tell Google you care about such an API.
