This paper presents a method for prototyping grasp-sensitive surfaces using optical fibers. In this system one end of a fiber bundle is attached to an image sensor. The other ends of the individual fibers are attached to distinct points of a surface. Thus the image sensor can detect changes in light reception caused by a hand covering the surface. By emitting infrared light through the surface and measuring the amount of reflected light the system can also recognize touch and proximity. Mapping between pixels on the image sensor and fiber positions on the surface is generated by a relative calibration method. This setup allows to quickly build grasp-sensitive objects without electronics skills. ACM Classification Keywords H.5.2 Information Interfaces and Presentation: User Interfaces General Terms Human Factors Author Keywords grasp recognition, tangible user interface, optical fiber, computer vision