It’s Fun to Know: The Portraits on Coins

You may not have noticed, but the portraits of presidents and other dignitaries on paper money are usually full-face views, while the portraits on coins are almost always in profile. Turns out it is difficult to design a recognizable frontal portrait on the thin surface of a coin. It is also difficult to replicate such a delicate design on the high-speed machines that mint coins.

(Source: The Straight Dope)