As stated in MDL-37984 comments, Picasa is being slowly replaced by Google+. Current API will be still be available, but from April 20th 2015 there's no deprecation policy. It's proposed to move Picasa related tools to plugins.

Note: don't forget to consider what happens with lib/googleapi.php once all uses are out.

Update: Google discontinued support for Picasa on 15 March 2016.