Add additional feature in Joomla admin panel

Add following features on my already developed website 1) Admin can create/remove category 2) Admin can add/remove photos from category (its not already built category feature) ---> category1 ---> picture 1 ---> picture 2 ---> picture 3 ---> picture 4 ---> category2 ---> picture 6 ---> picture 5 ---> picture 8 ---> picture 9 and so on...