Abstract: Automatic registration of an MR image is carried out in an image guidance system by placing MR visible markers at known positions relative to markers visible in a camera tracking system. The markers are carried on a common fixture which is attached to a head clamp together with a reference marker which is used when the markers are covered or removed. The tracking system includes a camera 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 with an array around the specific location to allow the processor is able to detect an angle of rotation of the pattern and to distinguish each marker from the other markers.