This was a very similar build-process. The mosaic was about the same size, it was built in a "studs-up" orientation (so the viewer is seeing the smooth sides of the LEGO bricks and plates), and a multitude of colors were used.
Actually, over the past decade LEGO has produced more and more new colors, so the color palette available for such mosaics has expanded. While the Mona Lisa mosaic used ten different colors, this project used twenty-one (the most colors I have ever used in a single project). It used about 7500 pieces, and is 74 bricks wide (and 262 plates high).
The links below document the progress of the build. In the picture at the upper-right one can see a couple of horizontal seams where I did not fully connect the bricks. This is because the three sections are about to be packed up and shipped overseas.
Back to Eric Harshbarger's main LEGO page.