The latest version of Picasa installs a separate utility called Google+ Auto Backup. It's a simple tool that lets you select the folders that you want to backup automatically and even has support for SD cards. Google+ Auto Backup works in the background, much like Google Music Manager and Google Drive for desktop.
Google+ Auto Backup uses your Google Drive storage and uploads at full size by default. You can change these settings any time in your Auto Backup Preferences.