You mean the box is ticked in a terms and conditions screen when you first turn the device on and that counts as opting in. It's on by default. Most people don't realise what it's doing until either the uploader drinks all their battery (which mercifully they seem to have fixed) or they have loads of photos pop up when they sign in to Gmail on a desktop.

The sign in process for Android devices has become ever more convoluted and incomprehensible. People, understandably, complain about the Facebook app, but Google are actually far worse.