I had an idea years ago using a webcam and the 'blood under fingernail' to have a trackpadless-trackpad (i.e. same as this project but on your table). Maybe so

I had an idea years ago using a webcam and the 'blood under fingernail' to have a trackpadless-trackpad (i.e. same as this project but on your table). Maybe some time-rich person will fork it and do so.