A system for detecting a position of an object such as a surgical tool in an image guidance system includes a camera system with a detection array for detecting visible light a processor arranged to analyze the output from the array. Each object to be detected carries a single marker with a pattern of contrasted areas of light and dark intersecting at a specific single feature point thereon. The pattern includes components arranged in an array around the specific location arranged such that the processor is able to detect an angle of rotation of the pattern around the location and which are different from other markers of the system such that the processor is able to distinguish each marker from the other markers.