Wow! What’s a funny thing? Do you ever think how a optical mouse works? Yes! You can turn your mouse into some kind of scanner or camera because it must have a optical sensor (mostly CCD).

People get bored sometimes, and when I get bored I sometimes open up stuff to find out what makes it tick. One time, I did this with an old optical mouse. Well, a mouse only has 2 chips inside: the optical sensor and a chip for the usb/ps2-interfacing. I looked up the datasheet of the optical sensor (which is an ADNS2610) and it told me the sensor has a tiny 18x18 CCD, which can be read out using the serial port (the one which normally interfaces to the PS2/USB-chip).
Optical Mouse cam

(via: Slashdot: News for nerds, stuff that matters)

For more information, you can download readmouse.zip to try your own on Windows. If you are on Linux, try parspi.c written by .