And James Cagney had a so called character face, even when he was young, so it should be rather easy to recognise him.

This is something I wondered too about the promos for the Faceshop or whatever software, it maybe a few years old: it worked with Winston Churchill. Churchill had one of the most famous character faces in the last century. You would even notice him when you see only his shadow. And that's what makes it difficult for faces who are less characteristically structured.