Picasa Web Albums is a service which allows users to maintain albums of their own pictures, and browse the albums and pictures of others. The API offers a programmatic interface to this service, allowing users to add to, update, and remove from their albums, as well as providing the ability to tag and comment on photos.
Access to public albums and photos is not restricted by account, however, a user must be logged in for non-read-only access.
For more information on the API, including instructions for enabling API access, refer to the Picasa Web Albums Data API Overview.
Authentication
The API provides authentication via AuthSub (recommended) and ClientAuth. HTTP connections must be authenticated for write support, but non-authenticated connections have read-only access.