I recently reinstalled Picasa and in doing so inadvertently turned on Google Auto-Backup. As I have rather a large number of images on my HD I quickly ran out of space in my Google Account. As this includes storage of emails for Google Mail that proved rather irritating.
I searched for a way to turn Auto-Backup off but clearly Google don't want you to turn it off so the advice is hard to find. Lots of red herrings with links to "How to turn of Google Auto-Backup " only to discover when you open the link the info tells you how to turn it ON but not OFF!!!
Eventually I found the advice I was looking for at this location link
Here are the instructions:-
Google+ AutoBackup? can be disabled, Uninstalled, or set to only back up certain folders.
AutoBackup gets installed automatically when you install or update to the latest version of Picasa.
Look for the AutoBackup icon in the system tray on the bottom right. It is pinwheel with 4 blades in the Google colors. It may be hidden, if so click on the up-arrow to the left of the system tray to show the hidden icons.It is bottom left in the image
Click on the pinwheel an select Settings...
Make sure it is signed in to your Google account associated with Picasa
Make sure the folders you want to backup are listed and selected, or unselect all of them if you don't wish to use autobackup at the moment.
You can also Pause AutoBackup if it is slowing something down too much.
To Uninstall Google+ Auto Backup:
If you don't want to use Google+ AutoBackup at all, uninstall it as follows:
Go to the Windows Control Panel.
Select Programs or Uninstall Programs.
Find and select Google+ Auto Backup in the list of installed programs.