Most sites using images do it very casually, without putting in a lot of thought. Why would they when the image is just something they picked up to drop into the post. It has not meaning to them and often it is pretty meaningless in the post too. It’s just what you are expected to do now. Every post should have an image. That’s what the so-called gurus say.
I wish sites would go back to the day when people created their own artwork to illustrate posts. If you don’t have a professional looking photo ready for the post, draw something yourself. Why does it have to be a photo if you aren’t a professional photographer work with what you actually can do.
Draw something or get into other forms of web graphics. Turn text into art. All you need is a graphics program of some kind and the ability to type letters into it and move them around. Experiment.