who needs to get a copyright?

Answer 1

People need a copyright who have written something, photographed something, etc. which they want to protect from commercial use by someone else.

Answer 2

under berne convention and in the USA, all creative works are automatically copyrighted once in fixed form. you only need a registration if you plan to defend your copyright in legal infringement actions. if you sell your rights, say to a publisher, then they will ask for a registration.