The implementation of an image-based sensor device able to track people in an indoor environment is presented. The primary objective of this paper is to prove the feasibility of a sensor capable of sub-metre level tracking accuracy and costing approximately US$20. Additionally, the proposed device is a valid solution for wireless multipath detection and mitigation problems caused by non line of sight conditions for radio wireless positioning systems. Under ordinary conditions, the proposed device is shown to be able to locate moving objects with an accuracy of some decimetres and with a coverage capability of about 30 square metres.