Rare might not refer to the painting itself. For example, if an artist had most of their work destroyed, any remaining paintings would be a rare painting by th

Rare might not refer to the painting itself. For example, if an artist had most of their work destroyed, any remaining paintings would be a rare painting by that artist. Or if a historically significant figure had only been painted by a small number of people, any painting of that person could be described as rare. It's probably fake anyway!