I have also faced the same situation so, I tell you some important points about that:
- whenever we insert a photo into the photo library, photo library create a unique URL for every photos that we insert. that means if we insert any image and delete that image and after we insert that image again, even if it is the same image, photo library provide a new unique URL.
- always remember one thing that there is no straight forward way to find the image is duplicate of previous images of not.
- photo library is not provided the facility to delete the image or asset programmatically from the ipone/ipad photo library.