Q: My storage use is too high (iphone 6s 64 gb)

I have a problem with the storage of my iphone 6s 64 gb. I only have the phone for a few months, so I really don't understand. It seems that storage is wrongly indicated.. It says that my pictures use 7,6 gb of my storage and that my mail uses 7,4 gb. I really don't understand, because I don't really have that much pictures on my phone. Just about 100 pictures, so I don't think that it should take up so many storage (7,6 gb). Also my mail uses 7,4 gb, which I mostly don't understand. I clear my mailbox every day on my phone and I don't even have large mails in it? Yesterday I tried to remove my e-mail account and when I restarted my phone, the 7,4 gb of usage was still there although I didn't even have anything on my mail app? I really don't understand, just like I don't understand how my 100 pictures can take up 7,4 gb? Could someone please help me? You can find the printscreen of my storage below. It is in dutch,because I'm from belgium.