General Auto backup folder

First disable Auto Backup under Settings - Accounts - Google Sync....
There might be actual copy of the photos on the phone, if possible clear them off.
Then, once done with that, go to Settings - More - Application Manager.
View "ALL" and look for Gallery. Open Gallery and press the "Clear Data".

Reopen the gallery to update thumbs for existing content.

Don't worry, clearing data won't delete any photos from your phone or SDcard.

 

You are most welcome

By the way, that kind of folders, are just mirrors of your Picasa and Google + galleries. They usually don't contain actual photos.
I would also suggest, if you have Google Plus account, to visit your account and explore galleries or photo albums. Chances are, your phone has uploaded your entire phone's gallery, to g+ Private gallery.
These galleries are never visible to anyone, unless you set it to "share" manually, each.
Given your Auto Backup was on, it could well be, all your stuff is on line