I have a Nexus 5 with Android 4.4.2, but I am confused as to where photos get backed up. First of all, in the Photos app (which is actually part of Google+), there is an option to set up Auto Backup. Now, in the settings under your Google-account syncing there is also an option to sync Google+ Photos. What is the difference?
Also, where are the photos stored? If you delete a photo from inside Photos or inside Gallery on my phone, does it get deleted from both places, from the web (if backed up), ...?
Also, what is the difference between the Gallery-app and the Photos-app?
Edit: Doing some tests with the auto-backup feature inside Photos, I've concluded: If you take a photo on your device and force auto-backup, it's available online as well. Removing it on your device keeps the picture online, and it is not shown in the Trash. Removing it online however DOES make it show up in the Trash, both online and on your device.
Deleting an auto-backuped picture online puts it in the Trash as well, ths making the image available twice on your device (in the Camera and Trash). Deleting it from the Trash still keeps the image in the Camera. Backing up the library does not upload that image again online, and the Cloud-icon remains.
Of course once you think you know the system it gets more complicated. Using Hangouts also puts those images inside a separate folder online, and for some reason some pictures only show up there and NOT inside the Auto-Backup folder. Perhaps because I've been messing around trying to figure thing out, I'll keep better note and force auto-backup in the future.
I guess it could be me, but this system is VERY complicated for a user. The cloud-icon would suggest to me that it's available online, but it's still there even after deleting the image online. Of course deleting it online means you don't want it. Also it's not really syncing if the images on the device are not the same as online. There can be images on the device but not online and vice-versa. And now I still don't know the difference between the sync of Google Photos and Google+ Photos...