'Inexistent' photos using up my iPhone's memory.
First of all, I'm using iPhone 5s 32gb. The content of this iPhone was entirely backed up (using iTunes) from my previous iPhone 4s, including photos, music, apps, etc. I just recently updated it into iOS 8.2 thinking that the update will somehow fix my problem but it didn't.
A week ago my iPhone gave me a warning that I was running low on memory so I thought that I need to delete some photos because I knew the photos are the one that takes up a large amount of my memories. I checked the camera roll and it said that I have around 3000-ish photos and 20~30 videos. So after backing up the photos and videos into my laptop, I deleted most of the pictures and videos manually until the camera roll said that I only have 482 photos and 6 videos. This is where the problem arised.
Apparently even though I've deleted so many photos and videos, I only got like 4gb freed up. I checked the phone's setting under 'about' and 'usage' tab and it stated that I'm still using 10.2gb for photos with 4755 photos and 38 videos. So basically, the info about photos and videos in the setting and in the camera roll doesn't match. It differs by a huge number.
My questions:
1. I wonder what happened?
2. Is it possible that it got something to do with the fact that it was backed up from my previous iPhone?
3. Can someone please explain to me what should I do?
I'm thinking of resetting it completely but if there's another easier alternative I would love to know that.
Thank you very much.
iPhone 5s, iOS 8.2