The basic concept is using a webcam to track multiple finger contacts. My preference is not to touch the display screen itself for day to day use - your hands get in the way of the display and it's not really comfortable to have your hands up in the air - and all those annoying finger marks! This is aimed at a desktop input device which could also potentially overlay a shadow of the hands as feedback. Three ideas come to mind frosted glass, optically dense liquid and a glass/gel/silicone samwich. Turns out all these and many more have already been explored. The core goal is to create a optical 'blob' you can track for each of the contacts. My blob tracking turns out to be a pretty quick way of doing this. Maybe a video for February?