My theory goes like this:
- He draws on a sheet of tracing paper which is on a pane of glass.
- The pencil or marker he uses is dark enough to show through the tracing paper.
- A camera is set up on the other side of the pane of glass and records the reverse side of what he draws - that's how you can see his hand behind the picture.
No. When you edit the video, you can mirror it. That turns everything back the right way.
So basically, he draws and we see exactly what he draws, the right way round, only we never really see his hand.