It’s not the greatest of art history mysteries, but if you haven’t seen this 4-minute YouTube clip from www.ted.com (an interesting boundary-crossing conference phenomenon you may not have come across) about how Siegfried Woldhek went looking for Leonardo’s face in his notebooks, I think you’ve missed out.
Most modern stories about Leonardo I’d advise taking with a pinch of salt (occasionally more), but this one’s perhaps just a touch more substantial. A simple idea, but one nicely followed through!
[Big restecp goes out to my artist sister Liz Jose for passing this link my way.]