If you use Linux, you know Xeyes is a simple program that follows your mouse movements. You can check out some web examples of Xeyes. You can even paste this javascript code on your website for Xeyes on the web.
Anyway, Hunz created physical Xeyes that stands on his window and follow people’s walking movements. Tight! We want one.
The eyes are made from large pizza boxes cardboard and rolled by RC-servos that are controlled by an ATTiny2313 that’s connected to the PC using the low-speed software usb stack. The camera is connected using USB as well. Since I disassembled my webcam and hooked it up to an FPGA for some experiments, I used an analog one and a USB video digitizer.
The video processing is done using mplayer. It’s cropped first to get only the street and no neighbour estates. Then a tiny & quick&dirty video filter plugin looks for the column with the strongest Y-component difference between the last & current frame and if the difference exceeds a certain threshold, that column is passed to the microcontroller using libusb.
http://zedomax.com/blog/2007/04/12/diy-linux-hack-xeyes/ 
