Face Transfer using the G'MIC plug-in for GIMP
Here is a simple and quick example on how to transfer a face from one picture to another, using the nice filter 'Blend [seamless]' of the G'MIC plug-in for GIMP !
This video runs in real-time, it doesn't take more than this to get the same result.
Get G'MIC for GIMP at : http://gmic.sourceforge.net/gimp.shtml