Wow this was way too hard to find. I had a photo on Google Plus that I did not want there whether private of not. It was a picture of my drivers license that did not need to be in the wild. Finding how to delete it was a trip. This was the site that helped http://www.vlogg.com/11373/how-to-delete-googleplus-auto-backup-photos/
Essentially when you are logged in to Google, go to this site
https://plus.google.com/photos/autobackup
and delete away.