A recent question concerning the president putting himself on the dollar got me to thinking: The US dollar at one time was printed with an appearance to celebrate aspects of education. I'm wondering if there are laws nowadays that require the dollars to depict significant historical figures like presidents, or if this sort of educational use for the appearance of US dollars is still possible under current law. In other words could the Secretary of the Treasury simply order the commissioning of such an "educational series" nowadays? Are nationalist political concerns pushing a mythologizing of the founding fathers the only thing preventing this?