Per provider, this API will be deprecated in January 2019. Developers are encouraged to migrate to the Google Photos Library API
From their site: The Picasa Web Albums data API allows client applications to view and update Picasa Web Albums content in the form of Google data API GData feeds. Your client application can request a list of user albums, photos, comments, or tags, edit or delete content in an existing entry, and query the content in an existing entry.
The following is a list of historical changes that were made to this asset. Typically,
once an API is published on ProgrammableWeb.com, the data we keep about that asset gets updated over the course of its life. For example, the endpoint or home page of the documentation might change.
As a means of enforcing the integrity of our data, every time a non-trivial change is made to the data we keep about an asset,
we require the entry of some changelog text before that change can be saved. This way, we have a great audit trail of all
activity surrounding the asset. For each asset, the changelogs begins with the moment an asset is approved for publication on ProgrammableWeb.
If you spot an error in our data and believe that a record needs to be updated in some way,
the ProgrammableWeb team would very much like to hear from you at email@example.com
08-12-18 11:59:53[Brief] Picasa Web Albums Data API to be Deprecated updated with Related API Google Picasa
05-06-15 15:52:33[Sample Source Code] Google Picasa Code Sample updated with Related API Google Picasa
05-06-15 15:47:29[SDK] Google Picasa Client Libraries by Google updated with Related API Google Picasa
30-05-15 11:38:51[Analysis] Why Google's Photos Announcement Has Subtle Relevance To Developers updated with Related API Google Picasa
21-01-15 17:05:59[Mashup] Magic Mosaic updated with Related API Google Picasa
25-09-14 15:30:32[Mashup] 55Photos updated with Related API Google Picasa