Add photos to Google+ Add your snaps ANDROID TIPS
For existing images that are already on your device, you can go through the laborious process of selecting them by hand and then use the Share icon to upload them.
However, if you are going to continue using Photos on a regular basis and want to tap into the Auto-Awesome/enhanced features the app offers, then the easiest/fastest method is to turn on ‘Auto-backup’ which automatically uploads your images/photos as you take them.
For new users, you need to log into the app first via the Highlights tab and then set how you want to back up (eg ‘Back up existing Photos and videos’) before tapping the ‘Turn on’ icon at the base. There is also an option to toggle the function on/off afterwards via the Camera tab or by tapping the Menu icon then Settings.
Source: Android Tips, Tricks, Apps & Hacks Volume 8 © 2014 Imagine Publishing Ltd