Voice Authentication for Classrooms?

USSJoin asks: "I am teaching a summer camp for gifted/talented children this summer, and one of my courses is an introduction to forensic science. One idea I had was to demonstrate voice printing and voice authentication. Using the magic Google, I was able to find software to get a visual representation of a voice print, but I didn't find anything that would allow me to demonstrate voice authentication. Ideally, I would like to be able to have students record their voices onto a cassette player, then speak into the computer, then try to fake out the computer using the tape recording. Does Slashdot have any ideas on how to demo this to brilliant young kids?"