> With photography, I've always had a hard time photographing someone who had dark skin. Lots of light needs to be used, and even then it needs to be filtered correctly, etc. This goes for any subject that is dark.

The issue does come down to a mix of (likely) inadvertent racism and physics.

It is very difficult to photograph people with darker skin. This is intentional, per Mother Nature. Very briefly, our atmosphere passes a certain bandwidth of colors to the ground. The peak frequency is in the yellow-green (this is why plants are this color usually). Unfortunately, one of those colors is in the UV frequency that just so happens to be the same frequency as the small channel of eukayotic DNA. Thus, cancer risk is raised when that UV photon energetically breaks up the DNA. So, mother nature evolved to co-opt the melanin molecule, which happens to absorb those UV photons, to help protect skin cells from this damage. Thing is, though, that melanin molecule also absorbs not just that UV color, but a lot of other ones. PhysicsGirl has a good video on how sunscreen works and what a freckle looks like under different wavelengths [0] that is informative here.

Now for the (inadvertent) racism. When they were first starting to make photographs, just about any photo sensitive material was 'good enough'. These, of course, were all in black and white. But, the frequencies/colors that these chemicals were photosensitive to, were much more than we can see with our eyes. It went from the low IR to the high UV, with all kinds of various notches and mixes in there. Tin-type photographs are a great example. During the US Civil war, there were a lot of pictures taken of slavery and 'colored' soldiers. It's not hard to distinguish the faces and features of these people [1][2]. One thing to note about these tin-types, look at the clouds, rather, the total lack thereof. That's an easy way to notice that the frequencies you are seeing in the photograph are not the frequencies that your eyes see.

When color photography started to become more widespread, the frequencies used for each color (CYM) and the absorptive bandwidth of each part of the color films were not accidents. They were chosen such that attractive young 'white' women in very heavy make-up and under very bright 1930's studio lights would be best seen. These color choices, due to the inherent racism of the times and other factors, were perpetuated into modern CCDs and CMOS chips we use today. There are important differences in the physics of digital and film color photography, but largely those original choices have been conserved.

One important difference is the IR spectrum pick-up. In most modern phones, the front facing camera does not have an IR filter on it. Next time you are near a security camera or at a toilet with those IR sensors, take a look at your phone using the front-facing camera. It should be straightforward to see the little blinking IR LEDs of these devices.

So, though darker skinned people are inherently difficult to photograph due to melanin and Mother Nature, it is not difficult to find the right frequencies that will work. It's a case of the 'lock in' effect that prevents this.

[0] https://www.youtube.com/watch?v=GRD-xvlhGMc

[1] https://www.pinterest.com/pin/385480049327844109/

[2] https://atlantablackstar.com/2015/01/05/7-things-about-the-f...

[3] https://www.pinterest.com/pin/126452702010324184/