How does fractal image compression work ? How can so much
information stored in so small files ? Does fractal compression work for other type of files ?
Here is an Introductory Overview.
Basically, it works really well for certain specific images, but it’s lousy (in addition to be lossy 
) for most others. Guess which images they show you when they want to brag?
It’s also incredibly processor-intensive, compared to, say, JPEG.