Hi IBG001,
It sounds like specific images are duplicated in Photos on your iPhone 5 with iOS 8. If you previously edited images in iPhoto for iOS and then migrated those images to Photos after updating to iOS 8, the article linked below provides information that may help you resolve the issue.
Migrating from iPhoto for iOS to Photos on iOS 8 - Apple Support
If you applied image adjustments to photos synced to your iOS device from iTunes, a duplicate of each photo will be created in Photos with adjustments applied.
If you weren't using iPhoto for iOS, take a look at this article to verify photo syncing is setup as expected:
iTunes: Syncing photos - Apple Support
Take care,
-Jason