The portrait is actually a recreation of one I did in 2005, and incorporates several learnings from the first go-around. The 2013 version here is based on a better known photo of Lincoln, and his face is more closely cropped to maximize the number of "pixels" used for defining his features. I also used a tighter penny tessellation (one with offset rows), which reduces the blank space between pennies and improves the quality of the image. The offset tessellation made placing the pennies a bit trickier, and I ended up writing a simple command line tool to compute the exact color and placement of each coin.