The picture of Newton was in green only, while the picture of Einstein was in red color only. Green and red light from the LCD projector are polarised perpendicularly with each other. As polarizer was rotated, it cut off either the green or the red so that only either Newton or Einstein comes into view.
Some 3D movies are made this way. The image meant for the left and right eyes are projected using two mutually perpendicular polarised light. The viewers are then given glasses which are fited with polarizers.