A system for registering a group of images of an anatomical region of a patient in a coordinate system of a medical system is disclosed. The system includes an object disposed in a known position in the coordinate system. In one embodiment, the object has a first state in which the object is visible in at least one image and a second state in which the object is invisible in at least another image. In another embodiment, the object is substantially invisible to the eye in each image, but detectable by image processing. The system includes an electronic control unit configured to process the images to identify an image location of the object, create a transformation model responsive to the image location and the known position of the object in the coordinate system, and register the group of images in the coordinate system using the model.