An example non-transitory machine-readable storage medium includes instructions to, when executed by the processor, capture an image of a face of a user viewing a display device, identify a light source in the image, and identify light from the display device reflecting off the face of the user. The example instructions are also executable to determine a signature of the light in the image by 1) positively weighting a light measurement from the light source in the image and 2) negatively weighting a light measurement emanating from the display device and reflecting off the face of the user. The example instructions are also executable to modify a display device setting based on the signature of the light in the image.