I'm in no way belittling your effort, but this guy looked so stock-photo-ish that it took about a minute to google him.
...And since i work with stock images often, I know the shutterstock
image license doesn't cover an image being reproduced more than 2500 times, and other redistibution-in-part restrictions are in there too, all of which nixes the use of their images for coin logos.
An original design involving a 3d human and protein chains would be most tasty though. I wanted to render protein coils in 3D for my design, but the numerous images from Stanford's folds proved material enough.