Copyright gives author or publisher legal ownership rights to control production, sale and distribution of particular documents or images.
Protecting your intellectual property is a vital part of creating and selling your own digitally published works.
Registering your copyright establishes a public record of your copyright worldwide.
An excellent resource on subject can be found at Brad Templetons site which I recommend as a must read by anyone interested in protecting their work...
When you run an online business be aware of copyright laws in other countries and compare them with your own country's laws and how they may also apply to you.
The information in government documents is usually not copyright and available for use by everyone, but always check to be sure.
When you have created your e-book you do not want an un-authorised party to illegally copy your work or claim it as theirs.
Along with other pirating proliferating on net stealing of ebooks is growing at an alarming rate.
There have been many cases where authors have found their work on other author's sites under name of other author. If your work is copyrighted you can at least legally sue for copyright infringement.