Shahriar Shahrabi writes:
A short break down of how to very quickly make a 3D model out of a painting using projection mapping. The process involves making a proxy geometry, projecting the painting on it and then baking that projection on a unique unwrap of the mesh for texture fixing . For portraits, given a pre existing head model, the process takes under an hour.
And the model is available on sketchfab for viewing and download: