This video is a little cheesy, but it shows the process clearly for transforming a room into a camera obscura.
One note of correction from last class: it's a song by Death Cab For Cutie (not Postal Service) that mentions how the eye sees images upside down. A Lack of Color enjoy the video below.
"And when i see you
I really see you upside down
But my brain knows better
It picks you up and turns you around
Turns you around, turns you around..."