ALL oics taken with the iphone are in the Camera Roll Folder.
ALL pics synced to your iphone from your computer are in Photos Library.
If you have enabled Photo Stream, then ALL Photo Stream Pics will be there.
You cannot get rid of these at all.
If you make albums in Camera Roll, then you will be able to access these photos from that album as well. No duplicates, simply two ways to get to the same pic - like an itunes playlist.
Same goes for albums synced to your iphone. You will be able to access the same photos that are in the Photo Library from the folders you choose to sync.No duplicates, simply two ways to get to the same pic - like an itunes playlist.