The following pages shows a typical process taken to complete an image in the digital form, from sketch. Below is a comparison image, that can be slide from side to side to see the way the digital art matches the sketch created firstly; of Mark Twain.
To the right of that is the animated gif of the entire process, to show how the steps are built up over time. This image of Mark Twain took only 6 hours (though they can take unto 10 to complete). The process, after base colour, always focuses on getting the eyes right first and then typically moving down the head.
If you look at the comparison image you will see a great deal of difference in the sketch to the final render. I guess this is a strong case of having faith in the observational skills and correcting as I go along. This was also very hard in this case, as the reference photo was not a direct on version of Mark Twain.
If you are interested in more animated gifs of the process, you can check out this page, here!