This was an experiment back in May, when COVID-19 was new and everyone rushed for thermal scans hoping they would reveal infections. Because I had it, I set up a cheap DANIYO HY-18 handheld thermal cam, and an Intel RealSense D435 cam to tinker with images, ultimately I wanted to locate the forehead.
Before I went off into detecting my own forehead from a 3D image, I assessed system accuracy. Primary sources are things that you may wear in front of your face, like face masks, or frames.
|no face cover|
|metal frame and face mask|
The results are off by around 0.75 deg C. This, of course, heavily depends on ambient temperature, this experiment took place on 2020-05-24, which had temperatures around 20 deg C, which would be a typical office or indoor setting.