The pin screen is a white screen embedded with thousands of headless pins, and is used for two dimensional animation. In order to create images, as seen on the right, the animator pushes certain pins all the way into the screen while pulling other pins all the way out. When a white light is shone crom the side of the screen, the pins sticking out create dark shadows, the pins all the way in create highlights, and the pins in the midde create varying gray tones.
Alexander Alexeiff and his wife Claire Parker designed the pinscreen in 1931 with the intention of creating a new technique for animation. After designing and building the screen, they filmed the first animation using a pinscreen called, A Night on Bald Mountain, presented here.
As you can see, the effect of the pin screen (which is also combined with some live-action footage here) was very different from what could be acheived with traditional and stop motion animation. In the following video, Alexander Alexeiff and Clair Parker demonstrate how they used the screen to create their pin images.
While the pin screen was never a widely used technique, it offered alternatives to traditional animation techniques of the time.