The finished piece. Below is my process.

First I start with traditional medium. The sketch is made roughly with a pencil.

I then scan the sketch and take it into photoshop. I use the brush tool to make "line art" and smooth out the drawing. I also add in a different color for for the background which will eventually be darkened.

The background color opacity is raised until it is the color I want. I move the line art layer to the top of my layers so it stands out neatly above the lighter grey I add underneath.

I then create a layer above the lighter grey which is a bit darker for the turtle's shadows.

I then add in color to make it pop a little and the design is complete.