Because iPhones and iPads continue to expand the storage capabilities of the devices the photo library has not kept up. Photos are stored as jpg files but are limited to 9999 before it roll overs and use the same number with duplicate number but with XXXX(1) as its file extension. If you delete a photo(s) the new photo(s) take the deleted number(s). Which means you have a duplicate number but different photo. I have 20,000 photos on my iPhone. I actual do delete photos but keep older ones on my computer. I periodically backup all my photos from my iPhone to my computer. The problem that I encounter is that file number XXXX wants to replace my previous XXXX jpg file. I want to keep both photos. Does anyone know a work around?