Simple graphical software for manually plotting fractals?

["Jordi Gutiérrez Hermoso" <jordigh@gmail.com>]

I'm teaching a numerical analysis course with Debian, and now the kids
want to be plot Newton fractals:

     http://en.wikipedia.org/wiki/Newton_fractal

Basically, all they want to be able to do is to manually plot the
fractal pixel-by-pixel. They're working in a blend of C and C++, so
ideally, I want to give them a C/C++ library that they can use for
this with minimum fuss. Extra options in the library that they can use
for saving their fractals in png format would be nice.

Suggestions?

- Jordi G. H.