> Multiple images of people of different color skins, and clothing styles should be used because nowadays it is very easy to over-tune your compression algorithm to a specific type of image or skin tone.
This is true. I have mentioned using different pictures to ensure not over-tuned for only one picture (I did not use those words, but thank you for mentioning, a better way to mention it). Different colours of skins and different clothing styles is one thing, but furthermore, you should not be limited to pictures of people, either (although some of them should be pictures of people, but not all of them); there are other living and non-living things to take pictures of, too.
This is true. I have mentioned using different pictures to ensure not over-tuned for only one picture (I did not use those words, but thank you for mentioning, a better way to mention it). Different colours of skins and different clothing styles is one thing, but furthermore, you should not be limited to pictures of people, either (although some of them should be pictures of people, but not all of them); there are other living and non-living things to take pictures of, too.