1. A gaze tracking system, the gaze tracking system comprising: an image sensor device positioned on or within a vehicle such that the image sensor device may capture an image of an operator interface area in the vehicle; one or more processors communicatively coupled to the image sensor device; and one or more memory devices, communicatively coupled to the one or more processors, including instructions that when executed cause the one or more processors to (i) perform a calibration and (ii) perform gaze tracking; the instructions to perform a calibration including instructions that when executed cause the one or more processors to: (a) transmit a signal to cause the image sensor device to capture a first image of an operator interface area in the vehicle, (b) receive the first image from the image sensor device, (c) detect in the first image three facial features of a person, the three facial features including two-eye pupils, (d) identify a first triangle including vertices positioned according to locations of the three facial features in the first image, and (e) associate the first triangle with a first gaze direction; the instructions to perform gaze tracking including instructions that when executed cause the one or more processors to: (a) transmit a signal to cause the image sensor device to capture a second image of an operator interface area in the vehicle, (b) receive the second image from the image sensor device, (c) detect the three facial features in the second image, (d) identify a second triangle including vertices positioned according to locations of the three facial features in the second image, (e) determine a transformation from the first triangle to the second triangle, (f) determine a second gaze direction based, at least in part, on the determined transformation from the first triangle to the second triangle by identifying a surface normal for the second triangle, wherein a change from the first gaze direction to the second gaze direction can be tracked regardless of whether the person's head pose changed from the first image to the second image, and (g) store, at the one or more memory devices, report data including data representing the second gaze direction.