something like this already existed and it produced very similar results.

hmmm. wikipedia turns up many http://en.wikipedia.org/wiki/Comparison_of_raster_to_vector_... but the one i was thinking of was potrace - http://potrace.sourceforge.net/

i've used potrace many times before - it works really well (i once hand-wrote some "powerpoint" slides, scanned them, then used potrace to make them appear "natural" - people thought i had made a font based on my handwriting!)

maybe it's the handling of colour that's new here? potrace only does monochrome images, as far as i know.