From left to right we have Maria Theresa of Austria, Otto von Bismarck of Germany, and Theodora of the Byzantines.
Imgur album with all the drawings, newest first, updated daily.
I originally picked historical rulers if only because there are so many paintings and photographs, depending on era, to use as reference, and then decided that the playable rulers of the Civilization franchise were as good a set as any other to work with. It’s certainly helping my drawing!