One hand holds the picture, the other uses the marker to separate the part.
Finger copy and move the image, and pen to write notes.
Double tear the screen image like a paper car in real life.
This software called Manual Deskterity is demonstrated by Microsoft on the Surface screen, but many people hope it will be included in the company's Courier tablet next year.
[youtube] http://www.youtube.com/watch?v=9sTgLYH8qWs&feature=player_embedded [/ youtube]
Video about Manual Deskterity