Apparatus, comprising: a magnetic tracking system, which is configured to generate a magnetic field in a vicinity of a body of a living subject; a probe, having a distal end configured to be brought into contact with one or more registration points on a surface of the body, and comprising: a contact sensor, located within the distal end and configured to output first signals indicative of a quality of the contact between the distal end with the one or more registration points; and a magnetic detector, located within the distal end and configured to output second signals in response to the magnetic field that are indicative of respective positions of the one or more respective registration points in a coordinate frame of the magnetic tracking system; and a processor configured: to receive a tomographic image of the subject, to verify, based on the quality of the contact indicated by the first signals, that the one or more registration points are valid; and to register the tomographic image in the coordinate frame of the magnetic tracking system using the positions of the one or more registration points that were verified to be valid; characterized in that the contact sensor comprises an electrode, and wherein verifying that the one or more registration points are valid comprises verifying that an impedance measured by the electrode on contact with each of the registration points lies within 20 kΩ - 40 kΩ when the impedance is measured at 20 kHz. a magnetic tracking system, which is configured to generate a magnetic field in a vicinity of a body of a living subject; a probe, having a distal end configured to be brought into contact with one or more registration points on a surface of the body, and comprising: a contact sensor, located within the distal end and configured to output first signals indicative of a quality of the contact between the distal end with the one or more registration points; and a magnetic detector, located within the distal end and configured to output second signals in response to the magnetic field that are indicative of respective positions of the one or more respective registration points in a coordinate frame of the magnetic tracking system; and a processor configured: to receive a tomographic image of the subject, to verify, based on the quality of the contact indicated by the first signals, that the one or more registration points are valid; and to register the tomographic image in the coordinate frame of the magnetic tracking system using the positions of the one or more registration points that were verified to be valid; characterized in that the contact sensor comprises an electrode, and wherein verifying that the one or more registration points are valid comprises verifying that an impedance measured by the electrode on contact with each of the registration points lies within 20 kΩ - 40 kΩ when the impedance is measured at 20 kHz. a contact sensor, located within the distal end and configured to output first signals indicative of a quality of the contact between the distal end with the one or more registration points; and a magnetic detector, located within the distal end and configured to output second signals in response to the magnetic field that are indicative of respective positions of the one or more respective registration points in a coordinate frame of the magnetic tracking system; and a processor configured: to receive a tomographic image of the subject, to verify, based on the quality of the contact indicated by the first signals, that the one or more registration points are valid; and to register the tomographic image in the coordinate frame of the magnetic tracking system using the positions of the one or more registration points that were verified to be valid; to receive a tomographic image of the subject, to verify, based on the quality of the contact indicated by the first signals, that the one or more registration points are valid; and to register the tomographic image in the coordinate frame of the magnetic tracking system using the positions of the one or more registration points that were verified to be valid; characterized in that the contact sensor comprises an electrode, and wherein verifying that the one or more registration points are valid comprises verifying that an impedance measured by the electrode on contact with each of the registration points lies within 20 kΩ - 40 kΩ when the impedance is measured at 20 kHz.