Instant Upload is one of the best features of G+. I can help you to stop it from doing it, but before I do, let me share some facts so you make the right decision.
Instant upload DOES upload all your photos and videos, but it uploads them to a private album that only YOU have access to. You then have the ability to move these photos or post them in a more public way.
Instant upload also gives you the ability to decide WHEN you want to upload (whether it's when you are out roaming about, when you are connected via wifi, or whether it's only when the phone is charging).
Any photos and video uploaded via Instant Upload do not count toward your Google storage quota (spread across docs/drive, picasa, gmail). You essentially have UNLIMITED storage of your photos and videos (
a few minor limitations-).
Lastly, people are much more likely to share photos and NOT lose them if you have them automatically synced to a computer (better yet, the cloud, like G+ is doing). Do yourself a favor and keep it on. If you lose your phone or it gets stolen, you will be happy you did.
Now, if you still want to turn it off, this is my recommendation:
There are 2 places you should look. The Google+ app settings page (most likely where you turned off the sync already)
and the Accounts and Sync settings page (found from Settings>Accounts and sync>youraccount@gmail.com> then uncheck Sync Instant Upload)
If it's still uploading your photos, you may want to consult the Google+ discussion forums.
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