How do I stop my photos from duplicating in my iPhoto library after importing them from my iPhone?

I'm using iOS 8.1.2 and iPhoto 9.6 and have spent a long time fiddling about with various different My Photo Stream and iCloud settings to stop this happening, to no avail. I mainly use the Oggl app but the duplication of my photos still happens even if I just use the iPhone camera. It also seems to leave around 0.5GB of photo files 'dormant' in my iPhone's Other memory which disappear when I do a system restore but return after consecutive photo syncs.