Public Domain Images are available for public use. For instance, pictures taken when working for the U.S. government or any pictures that you can download from a government website are automatically public domain.
Right Protected Images are bought for a certain length of time for a certain project. These images are usually negotiated beforehand with the photographer, and for a fee, you will have exclusive rights to the image during the arranged time period. While good for big businesses, these are not very effective for website designs.
Royalty Free Images are also purchased, but after the one-time fee, you can use the image however you like.
Creative Commons licenses are designed to give copyright holders a range of permission options for digital intellectual property and in most cases allow educational uses (for example, many of the images on Flickr and Wikimedia Commons).
Give the author of the image proper credits (Attribution) even when it is in the public domain.
When dealing with freely viewable collections on the internet, look for a page with copyright information, a license statement, terms and conditions, or permissions. This page may give blanket permission for educational purposes, instruct you to check copyright terms for each image, or ask that you contact the image owner for permission to use it. In other cases, you may be required to pay a usage fee.
Make sure you understand the license correctly
If an image is copyrighted you must obtain the permission of the copyright holder of an image before using, reproducing, or manipulating it.