Building a tree of images

Here comes my current C++ assignment.I just glance through the spec for my latest C++ assignment and guess what?Things get even more tedious and interesting this time.I have to build a tree of images! How can this be done? The basic idea is to let the root of the tree to be the whole image and the tiny little pixels of the image to be the leaves for the tree. I was fascinated by the fact that people actually come up with this novel kinds of idea to represent colorful images in different ways. For my last assignment,I was told to represent the image using a list. Now, I learned a more efficient way to manipulate my image - using a tree. It seems to me that people have to struggle to make their program as efficient and as fast as possible. Is it that important to have greater speed in everything? Sigh....I just hope that I can complete this assignment as soon as possible.