How to get a copyright is determined by the laws of governments.
There is no "international copyright" but treaties and conventions provide rules and regulations for how you get a copyright in most countries.
However, like patents, governments do amend their copyright definitions, their rules, and regulations, either because of court decisions or for economic considerations.
For example, some literature that is copyrighted in Europe is not recognized as copyright in the United States. Similarly, what may be considered copyright in the United States is not recognized as copyright in China.
In the United States, the style of printed characters (typeface) cannot be copyrighted, but they can be in the United Kingdom.
In some countries, the three-dimensional configuration of a microchip is protected by copyright, while in other countries it is protected by a separate property right known as "integrated circuit topography".
How To Get A Copyright
In most jurisdictions, you do not have to register a copyright with a government. How you get a copyright is merely by expressing an original work. The right is automatic and your copyright is also recognized in other countries because of treaty conventions.
However, a government may require you to obtain a certificate of registration if you decide to enforce your rights in court.
Similar to patents and trademarks, a copyright gives you the privilege of enforcing your ownership by suing or threatening to sue somebody.
It is tool used to minimize competitors seeking to compete with you by copying you.
Examples of what qualifies for a copyright can be read by following the link at the bottom of this page.
What You Cannot Copyright
Copyright is for specific expressions and not for ideas, information or facts.
You cannot copyright an idea for a movie, book or invention but you could copyright a script, novel or instructions.
Ideas, information and facts are considered public property or "public domain" and is available to anyone.
The "public domain" includes any creative work that has expired rights or that is not otherwise legally restricted for use by the public.
You cannot copyright anything that is in the public domain.
Brief word or sound combinations, titles, names, plots, slogans, characters or creative marks are not generally covered by copyright but may be protected by trademark.
A copyright covers "work" that is a more substantial in content.
If you create a "work" for someone else for which you received compensation, the copyright is owned by the employer. A person who contracts for creative work in exchange for remuneration is the owner of the creation whether it is for literature, art, photographs, engravings or music.
What Is Infringement
If you copy, reprint, record, distribute or perform a creative expression belonging to someone else without their permission, it is an infringement of their copyright.
Fair Use Of Copyright
In many countries, there are exceptions that allow others to copy your "work".
A "fair use" or "fair dealing" of your copyright is permitted if that use is for a particular purpose such as research, private study,education, critical reviews or for allowing access for the visually impaired.
It is generally accepted that "fair dealing" users must provide the source of the work and/or the name of the author.