I am unsure how important this is for you, because I can't imagine what you tried before asking here.
This[
^] will get your video on your WPF form from your webcam. As I said, in WPF you can draw anything you like on top of the integrated video control.
This[
^] is a Microsoft sample on how to create a drawing program in WPF. Combined, these two google searches took me less than a minute to find.