How do authors add in "title pictures" to their chapters?

CSIDE for windows:)
how do authors add in those fancy lil title pictures(?) at the beginning of their books? I’m assuming its some kinda png, transparent background with text in front of them. how do they make them? like, is there a specific app? and how do they get it to change from dark mode/light mode?

Here’s an excellent guide to doing exactly what you’re looking for.

a header!! that’s the word!! thank u very much!!

No problem. Take a look at the post N 22 to see more variants for different background colors.