Your photos are stored on Google, and if for some reason you want to delete these photos stored on Google and disable the automatic backup feature for future uploads, you can do the following:
Step 1: Launch the Google + app.
Step 2: Tap on Menu and select Settings.
Step 3: Click on the first item in the list which is automatic backup, and select it.
Step 4: Your Google account is currently set to backup, toggle the switch to Off to turn it off.
Step 5: Go back to settings and navigate to your Google account.
Step 6: Click on delete account and uncheck the Sync photos with Picasa option.
Step 7: Access the website http://picasaweb.google.com, log back into your Google account, and you'll see your previously synced images. Select all or the ones you don't like, delete them, then return to your phone and log back into your Google account as before. Everything will revert to its original state (contacts, calendar, apps, including auto backup images). However, at this point, auto backup images will only contain the ones you haven't deleted.
https://Mytour.vn/delete-auto-backup-photos-on-android-1151n.aspx
So there you have it, we've guided you through deleting Auto Backup photos on Android. Follow the instructions, it's quite simple. Additionally, to make your photos look even better, you can use the Photowonder app for editing.
