This works for my S 4. Go to your Dropbox folder on your phone and click on the menu button. Click on Settings. There you will find an option to "Turn off Camera Upload". You won't get any of your camera photos sent to Dropbox, but you won't get any duplicates either. This isn't a problem for me as the bulk of my phone photos aren't worth keeping forever anyway. The ones I do want to keep I download to my computer and go to Dropbox from there with only my "keepers".