Be sure you understand the concept of "fair use" before you use or repurpose image files into your work.
Fair use is generally defined as the allowance to use copyrighted material in a fair manner without obtaining permission from the copyright holder. For educational purposes (research papers, classroom presentations, etc.) always cite the original work! This may take the form of in–text citations, a references page, an addendum to presentation, etc. If you are planning to use your work beyond the classroom (educational), on the web, for commercial (for-profit) purposes, etc., you should obtain permission from the copyright holder for all copyrighted works used in your work (including derivative uses); not obtaining permission is a violation of US copyright.
There are four factors that impact the justification for Fair Use (Section 107 of US Copyright Law).
1. The purpose and character of the use, including whether such use is of commercial nature or is for nonprofit educational purposes. This refers to:
Whether the work is for educational use, whether there is profit from the use of the work, whether the use is credited (cited), level of access to the work, whether the use is for criticism, commentary, or news reporting, how derivative the use of the work is.
2. The nature of the copyrighted work. This refers to:
Whether the work is published, how creative the original work is, whether the work is fiction or non-fiction.
3. Amount and substantiality of the portion used in relation to the copyrighted work as a whole. This refers to:
How much of the original work is used, how important the portion used is to the original work.
4. The effect of the use upon the potential market for or value of the copyrighted work. This refers to:
Whether the use will impede or prevent the copyright holder from profiting from their work.
A good rule of thumb is to check a website for specific guidelines on permissions. Websites with image content that is copyrighted will usually state the parameters that they consider fair use for their content. Read this information to better understand how to cite the content you are using. Again, always cite your sources.
This page was adapted from the site on Visual Resources developed by Dan McClure and Tricia Juettemeyer at: http://sites.google.com/site/budgetvr/