1. A method of correcting for movement of a reference object within an image detection field of an eye tracking apparatus said method comprising: providing said eye tracking apparatus, said eye tracking apparatus including a first image detector for capturing scene images, a second image detector for capturing eye images including a pupil of said person and a processor for receiving said scene images and said eye images and outputting eye tracking images, each of said eye tracking images including a gaze point corresponding to a line of sight of said person, said first image detector and said second image detector being coupled to a wearable accessory and being fixed relative to one another; mounting said wearable accessory on said person; identifying said reference object, said reference object being a marker applied to the skin of said person and being located within said image detection field of said second image detector; performing a calibration method and generating a calibration mapping, said calibration mapping for mapping pupil location within said image detection field to said scene images; capturing said scene images and said eye images; determining a location of said reference object within said image detection field on each of said eye images; applying said calibration mapping to each of said eye tracking images and adjusting said gaze point on each of said eye tracking images to correct for movement of said reference object within said image detection field; wherein movement of said reference object within said image detection field corresponds to movement of said wearable accessory relative to said person.