Here is a timelapse picture of the process of creating one of these artist's portraits in digital pen and ink.  This particular example shows Vivian Carol who recorded for Merben Records of Philadelphia.  Vivian is shown with the famous Independance Hall in the background.  This demonstrates the various stages in what is a process taking days compressed into seconds.  Whilst digital artistry helps avoid some of the pitfalls of other mediums, as it is relatively easy to rectify errors; it comes with additional challenges.