tutorials on mapping and creating new hair texture?

Hello I was wondering if anyone knew how, or if there was a tutorial already, for mapping hair onto texture properly. All i've seen is how to edit/retexture existing texture or how to mesh hair from scratch with almost no instruction on the texture part. I've tried just importing a basic photo of hair texture which works, but it's not as realistic as i'd like. I'm completely confused on how people create those strands/pieces of realistic hair and how they map them, vs having one big imported photo if that makes sense. I'll try to link what i'm working on as examples of what i'm talking about. photos

package

blender file