It can be done with a sound recording of the tapping of the keys too: http://www.cs.utexas.edu/~shmat/courses/cs6431/zhuang.pdf http://www.cs.utexas.edu/~shmat/

It can be done with a sound recording of the tapping of the keys too: http://www.cs.utexas.edu/~shmat/courses/cs6431/zhuang.pdf http://www.cs.utexas.edu/~shmat/courses/cs6431/zhuang.pdf