From Google:
Copyright Is Automatic?
Yes, thanks to the Berne Convention. At the moment of creation, when the artwork is "fixed" in some tangible form, copyright applies automatically. For a photographer, when you press the shutter release you are making a photo and gaining copyright to that photo at the same time. You don't have to declare copyright or file any paperwork. It is yours to keep until you explicitly give it away or you die (copyright expires after you, the duration in the U.S. is the author's lifetime plus 70 years).
That said, there is an advantage to filing for copyright. If a dispute arises, you can get punitive damages (in addition to compensatory damages) if a form was filed before infringement.
What Is Not Covered By Copyright?
It's important to note what is not covered by copyright.
Copyright covers form but not idea. It applies to the tangible artistic result -- known as the "form of material expression" -- not the underlying concept. So your photograph has copyright, but not the idea or viewpoint behind it. For example, if you take a great photo of some natural thing, such as a beach or Yosemite Valley, you can't stop other people from taking the same photo.
Some things are in the "public domain" and are free for the people to use. This includes artwork published before 1923; copyrights that have expired (complex); and public property such as written laws.
Copyright does not apply to facts, since these are universal not individual. Factual dates and figures can't be copyrighted, but text expressing those facts may be.
Copyright can expire. In the U.S., the duration is lifetime plus 70 years.
Copyright does not prevent resale. In the U.S., after the "first sale", the owner can resell a work as-is (the work can't be copied or resold in an altered form).
Copyright may be superceded when other laws apply, such as trademark or privacy.
Fair use is permitted. This is complex, see below.
Fair Use
Fair Use (or Fair Dealing in some countries) permits copying for some purposes, but is a complex issue. Generally, copying is permitted for personal use, research, teaching, criticism, parody, news reporting and editorial use.
Beyond that, the law is deliberately vague and is decided on a case-by-case basis. A lawyer can render an opinion, but there's no accurate answer until a case is adjudicated by a court. Questions include: how commercial was the use, has the market of the original work been affected, how different is the derivative work, has a significant amount of work been copied. Note that "fair use" is an "affirmative defense", where the infringer has the burden of proof to show that the use was indeed fair.