Since pictures of natural objects can be modeled by fractals, it makes compressing pictures in terms of fractals very useful. One way is to define fractals as processes or images that exhibit self-similarity . In other words, reduced versions of the fractal appear throughout the fractal. For instance, look at the fractal fern below. Each branch of the fern is a reduced version of the entire fern.
Many natural objects have parts that are similar to other parts of it, like the fern.
This is just the beginning of the usefulness of fractals. Many phenomena like heart beat, turbulent weather, the stock market, and mountains also exhibit self-similarity. Other great example of fractals are landscapes. The picture below is a mountain generated using fractals. Fractals are excellent at creating realistic images, because they can model natural objects well.