Copyright infringement occurs when someone other than the copyright holder copies the “expression” of a work. This means that the idea or information behind the work is not protected, but how the idea is expressed is protected. For example, there have been many movies about Pirates, but only one Jack Sparrow.
Copyright infringement can occur even if someone does not copy a work exactly. This example of copyright infringement is most easily apparent in music and art. Copyright infringement occurs if the infringing work is “substantially similar” to the copyrighted work.
To fully understand copyright infringement, you must understand what rights you hold as a copyright holder. You own more than just the rights to reproduce the work filed with the US Copyright Office.
An owner of a copyright owns a “bundle” of rights. Each of these rights can be sold or assigned separately. Copyright infringement occurs when one of those rights are used without the express consent of the copyright owner. The rights owned by the owner of a copyright include:
The Right to Reproduce the Work. This is the right to reproduce, copy, duplicate or transcribe the work in any fixed form. Copyright infringement would occur if someone other than the copyright owner made a copy of the work and resold it.
The Right to Derivative Works. This is the right to modify the work to create a new work. A new work that is based upon an existing work is a "derivative work." Copyright infringement would occur here if someone wrote a screenplay based on his favorite John Grisham book and sold or distributed the screenplay, or if someone releases or remixes of one of your songs without your consent.
The Right to Distribution. This is simply the right to distribute the work to the public by sale, rental, lease or lending. The music industry lawsuits targeting file-sharing web services claim that these services violate the right to distribution held by record labels.
The Public Display Right. This is the right to show a copy of the work directly to the public by hanging up a copy of the work in a public place, displaying it on a website, putting it on film or transmitting it to the public in any other way. Copyright infringement occurs here if the someone other than the copyright holder offers a work for public display.
The Public Performance Right. This is the right to recite, play, dance, act or show the work at a public place or to transmit it to the public. Copyright infringement would occur here if someone decided to give performances of the musical "Oliver!" without obtaining permission from the owner.
There are three exceptions to the copyright infringement rules, which allow one to reproduce another's work without obtaining a license or assignment of rights:
Fair Use. This is a doctrine which permits the reproduction of copyrighted material for a limited purpose of teaching, reviewing, literary criticism and the like. Without the “fair use” doctrine, books and movies could not be reviewed and colleges and high schools would not be able to study works by people like Arthur Miller. This is also how television programs such as The Daily Show are able to use copyrighted material in their commentary. "Fair use," however, is determined on a case-by-case basis.
Public Domain. This refers to works which are no longer covered by copyright law. For example, the song “The Star-Spangled Banner” can be performed without ever paying license fees to anyone because the copyright has expired.
Non-Copyrightable Works. Copyright infringement cannot occur when someone uses material that cannot be protected by copyright, such as facts or ideas. However, if someone puts a bunch of facts into the form of a book (e.g. The Farmer’s Almanac), copying all or part of that book would constitute copyright infringement.
The most important first step you can take to avoid copyright infringement of your own work is to register your work with the US Copyright Office. If you discover that there has been copyright infringement involving your work and you haven’t registered with the US Copyright Office, you won’t even be able to commence a lawsuit for the copyright infringement until you have registered the copyright to your work. Thanks : http://www.clickandcopyright.com