Geography and income are two powerful conditioners. These can leak in so many ways: uncropped background (geography), image color and quality (income), eyeglass shape (geography and income). This study really needs more controls. Geography and income would be a nice start.
But then the data wouldn't represent the natural world: nature as it is.
Raw data is the correct thing to use, because it's what a hypothetical other person would also use if you ran the same experiment yourself.