Remote Interactive Whiteboard (Projector+Camera)

I'm looking for software that can use a projector to "illuminate a
whiteboard" with white light.  Then let local or remote computer users
"draw" on the whiteboard by masking the projected white with black or
color.  Local users could still use dry-erase markers too, and It
needs to be able to take snapshots of the board, compositing the real
world markings and digital markings (Though a still of the remote
video would work).

Has anything like this been polished at least to the 50% stable mark?

What projects should I look at?

That laser-grafitti program is similar to what I want, except I'm fine
with the only digital input being a mouse cursor.  The only need I
have for the camera, is so that local dry-erase markings can be
shared/captured.

I'm also looking for suggestions for GNU video-switching software.
Attach 4-6 usb cameras, and mics.  Then mix all audio, and tile all
video, until one mike is X percent louder than the rest, which would
cause its corresponding camera to go fullscreen.
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