In the United States, copyright is a "form of protection provided by the laws of the United States to the authors of 'original works of authorship' that are fixed in a tangible form of expression"[1].
Copyright protection in the U.S. is automatically given to the author from the moment the original work is fixed.
The full U.S. copyright law was established in the Copyright Act of 1976.
An original work of authorship is defined as "a work that is independently created by a human author and possesses at least some minimal degree of creativity"[1].
This includes:
Literary works
Musical works, including any accompanying words
Dramatic works, including any accompanying music
Pantomimes and choreographic works
Pictorial, graphic, and sculptural works
Motion pictures and other audiovisual works
Sound recordings, which are works that result from the fixation of a series of musical, spoken, or other sounds
Architectural works
Software
Examples of work fixed in a tangible form include:
Photographs
Poems
Paintings
Dances (if they are written down or recorded)
DVDs
Movies along with their music
Even a doodle on a scrap piece of paper
Some things are not protected by U.S. copyright. This includes[1]:
Ideas, procedures, methods, systems, processes, concepts, principles, or discoveries
Works that are not fixed in a tangible form (such as a choreographic work that has not been notated or recorded or an improvisational speech that has not been written down)
Titles, names, short phrases, and slogans
Familiar symbols or designs
Variations of typographic ornamentation, lettering, or coloring
Listings of ingredients or contents
No, there is no global copyright agreement. Each country has their own copyright laws that may differ from the U.S.
This document created by the U.S. Copyright Office provides more information on international copyright agreements.