Why do the 400 pictures on my IPhone take up 5.9 gigabytes of memory?

I have tried deleting many pictures and it only seems to clear up a little bit of memory, this just seems way to high for me.

This makes no sense… I used to have over 2, 000 pictures, and it didn't even take up 3 gigs.

There's something wrong… I'd try contacting Apple and asking them why so many GB is wasted from pictures.