Oh man this gets better. Seems the Diffused Illumination techique in my last post is really known as Rear DI. Effectively you are creating a beam of IR light and blasting out the box through the opening at the top. Your camera ( in the box ) looks for the light gathering (scattering?) where you are hands are on the acrylic and the software does the rest.

Now things get funky....

Role on the other type of DI - Front DI. This technique uses the natural ambient IR light that exists in the environment. This means that there's no need for any IR lights in the box at all..

So, my "list" of box items is.... a webcam (with filters etc), a backlight for the tft panel... and er.. that's it!. (it can't be this easy surely!)

Front DI is gonna get tested soon....