If you are a Picasa user, you will notice that the latest version of Picasa for Windows installs a new utility called Google+ Auto Backup which lets you select the folders of your photos that you want to backup automatically. It works in background similar to Google Music Manager and Google Drive for Windows. The full size photos use your Google Drive storage (15 GB). You can switch to standard size (2048px or less) for the unlimited space from Google.
Google+ Auto Backup is separate from Google Picasa and has it's own Uninstall entry under Programs and Features in the Control Panel of Windows.
All photos uploaded through Google+ Auto Backup will go to a private album in Google+, so you can decide what actions to take once they are backed up to Google+.
Right now, the only way to get Google+ Auto Backup is to install Picasa.