Abstract: A system for detecting an amount of force applied to a finger where the back upper portion of the finger is illuminated by light. The system includes intrasubject and intersubject registration. Another embodiment relates to using linear discriminant analysis to generate a fingertip force model and obtain a force measurement. In other embodiments, the system is used to mimic the input of a mouse, a track/touch pad, a keyboard device, or control a robot. In other embodiments, the system is used to assist in physical therapy, medical diagnosis, medical studies, or contact measurement.