I am looking to have some work done on my hairline. I am very concerned about having a natural-looking result.

I am looking to have some work done on my hairline. I am very concerned about having a natural-looking result. I can look at pictures of guys who had hair transplants and say this one has a natural hairline or this one does not but how is this achieved? What are the characteristics that make up a natural hairline and how is this achieved through surgery?