I followed the awesome tutorial proposed by Breno Bitencourt
Except I only use illustrator, I Import the photo and lock the layer.
Then within a new layer I draw raw polygons using the pen tool ("p"), make sur the vectors cross.
I select everything ("ctrl+a") and use the Shape Builder Tool ("shift+M"') to make sur each polygon is an object.
After that I select the polygons using ("v") and then use the Eyedropper tool ("i") to extract the color from the photo underneath and apply it to the polygon.
Sometimes it's not easy to select a polygon if the neighboring polygons are already in color, so I select both the contour of the polygon I want and the neighboring polygon and unselect the neighbour with shift key and then use the Eyedropper tool.
