Public Domain versus Creative Commons
When you are adding images, videos and other content that you did not create to your presentation, it is important to make sure that you are not violating anyone's copyright. One way to do so is to nd public domain images for your presentations. The site from the United States - Copyright.gov - explains the public domain as follows: "A work of authorship is in the “public domain” if it is no longer under copyright protection or if it failed to meet the requirements for copyright protection. Works in the public domain may be used freely without the permission of the former copyright owner." Because such works can be used without first seeking permission, they are ideal for many projects, particularly those that will extend beyond educational uses.
Note: Even if a work that you use is in the public domain, must provide attribution for the work.
If you can't find Public Domain media that meets your needs, you can also use Creative Commons-licensed content as long as you ensure that you correctly attribute this content to its creator and otherwise meet the terms of the license under which the image is offered. You can find more information about this on the Creative Commons FAQ.
The following resources will help you find public domain images for use in your project. These are not the only sources for public domain materials but it's a good place to start. Make sure you always credit the image.
Bing - Search using Bing Images and then limit your results to Public Domain images by clicking on "License" in the menu below the search box and selecting Public Domain.
Flickr - Flickr includes an option to mark media uploaded to the site as being in the Public Domain. Though currently only a limited number of items bear this mark, this content is sure to grow over time.
In addition, Flickr maintains The Commons, which offers access to images no known copyright restrictions from over 70 institutions ranging from NASA to the National Library of Sweden. In almost all cases, the images have already entered the Public Domain for one reason or another. Users can limit their image searches to a specific institution by navigating to an institution's photostream and then selecting that option from the dropdown options that appear as the user types a search into the search box.
From Visually.