Touch screens have become increasingly popular and widely used in most human-computer interfaces. As screen sizes have become larger for commercial use, the cost-performance ratio has been an important issue for both producers and consumers. In this paper, we present a new low-cost touch display method using an optical technique. Our approach is suitable for any regular screen without size limitation and represents a cost-effective solution. The proposed system employs a single webcam and an infrared laser line projector and incorporates image processing and computer vision methods to achieve the desired touch function. The experimental results of the proposed method provide a novel, real-time, and low-cost system to transform a conventional non-touch display into a touch-sensitive screen. The infrared optical technique can implement touch interactivity on desktop screens or large projection screens. Additionally, users can set up the system easily.