Note:On April 20, 2012 Google announced that they were deprecating Picasa for Linux and will no longer maintain it on that operating system.
To install picasa 3.0 on ubuntu 12.04
1.Go to picasa download page and download the deb package file (32-bit).
2.Double click the .deb package file or open with ubuntu software center and click the install button.
3.Type your ubuntu password if needed and wait until the installation is complete.
4.After the successful installation,click the Dash home from unity launcher.And type picasa in the search field.Then click picasa.