Converting photos to paint by numbers?

[indigo-red.livejournal.com]

I was curious, about 2 years ago there was a Trading Spaces boys vs girls episode I watched from my sofa when the remote control was too far away.

They took photos of animals and converted them to paint by numbers canvases and then painted them. i've always been seriously curious how this worked and would be extremely pleased to find out. It's been on my mind for this long, I thought I would pose the question here.

Any info or suggestions would be greatly appreciated.

Thanks!