In January 2019, Google is deprecating its Picasa Web Albums Data APITrack this API and disabling all associated OAuth scopes. Any existing applications using the API will continue to work until that time. In March 2019, the Picasa Web Albums API will be turned off at which point all calls will fail.
The Web Albums Data API allowed developers to integrate their applications with the since retired Picasa web service. The service was retired in 2016 as Google chose to focus on Google Photos. Applications that are using the Picasa API should migrate to the Google Photos Library APITrack this API in order to continue working.
Developers can refer to the migration guide for more details.