David Arnott wrote on Nashville Business Journal about Google Photos uploading photos even if you don’t want it to.

Five weeks later, on a whim, I figured I’d see if Google Photos had made any tweaks and re-downloaded the app. Instead of my pair of test photos, I saw hundreds of images. They weren’t synced from my phone in that moment, because I always delete photos from my device once they’ve been uploaded. My phone must have been uploading pictures to Google Photos even though I didn’t even have Google Photos on my phone. […]

All I had to do to turn my phone into a stealth Google Photos uploader was to turn on the backup sync, then uninstall the app. Whereas one might reasonably believe uninstalling the app from the phone would stop photos from uploading automatically to Google Photos, the device still does it even in the app’s absence. Since making this discovery, I have re-created the issue multiple times in multiple settings on my Galaxy S5.

I reached out to Google, and after reaching someone on the phone and describing the issue, was told to wait for a comment. Several hours later, I received a terse email that said, “The backup was as intended.” If I want to stop it from happening, I was told I’d have to change settings in Google Play Services.

Be careful what you’re getting yourself into with a free app. If you’re not paying, you’re the product.