[TempSwee]

Don't take pictures in HDR, It takes a lot of space.
Make sure that there is no hidden albums.
And look if you got videos in the pictures.
There is some videos that takes a lot of space.
Check with iTunes and with your iPhone
PM if u want more help!

[TempSwee]

Connect your iDevice to your PC.
Don't open iTunes, Check "This Computer" and check the Image folder there.

Sometimes pics gets hidden.