Method for verifying registration of a model of an internal-body-part with the internal-body-part in a reference coordinate system. The internal-body-part is at least partially unseen directly by a user. The method includes the procedures of continuously determining a position and orientation of a head-mounted-display in the reference coordinate system, determining a display location of at least one virtual marker, and displaying the virtual marker according to the display location. The display location of the virtual marker is determined according to the expected position of a respective at least one reference point relative to the head-mounted-display. The reference point is directly visible to the user. The relative position between the reference point and the internal-body-part is substantially constant. The position of the reference point in the reference coordinate system is predetermined. When the model and the internal-body-part are effectively registered, the reference point and corresponding virtual marker appears visually in alignment.