Although copyright law has many exceptions for educational purposes, there's a big difference between what you can do in the classroom and what you can do outside of the classroom. When you are in the classroom, you are free to perform or display any copyrighted works that you have legally obtained. Playing videos and music, displaying images in your presentations, reading texts aloud—all of these are examples of things you can do in the classroom without any restriction. You can also include copyrighted content in homework assignments or papers you write, but be sure to attribute them properly. However, outside of the classroom, you are more limited in what you can do. This is especially important to keep in mind if you plan to copy and republish copyrighted works on the open web.
Not everything you find on the Internet can be copied and reused without restriction. Even if you do not see a copyright notice, it is likely that the work is copyrighted. However, there are many resources you can use to narrow your searching to content in the public domain or content that is available under a Creative Commons license.
If a work appears online with a statement that it is licensed under Creative Commons or in the public domain, you should still consider whether or not these claims are trustworthy. Doing a small amount of research on the work's origins or avoiding using works that are clearly copyrighted (for example, works from recognizable publishers or corporations) in nonpermissable ways will help you avoid infringing copyright.
What kind of licensed work you’re looking for will depend on how you want to use it. Do you want to simply copy and republish an image on your web page? If your use is noncommercial and you won’t be creating a derivative work, you can use any Creative Commons licensed content as long as you attribute it to the original author. Do you want to edit or remix that image? You’ll need to find a work with a license that does not restrict the creation of derivative works. If the work you want to remix has a “share alike” license, you’ll also need to be sure to license your new creation under the same terms. Below you'll find three examples of resources you can use to find open content on the web.
Search.CreativeCommons.org: A search platform created by Creative Commons that lets you search multiple sites for Creative Commons license images, video, music, and other media based on the type of use you want to make.
Wikimedia Commons: A repository of public domain and freely-licensed educational media content. Everything is free to use, but for all media not in the public domain, you’ll need to check the license and comply with its terms.
flickr: A repository of images and video that allows you to filter your searches for content you are free to use. Using the drop down filter in the upper left corner, you can search for works in the public domain, all Creative Commons licensed images, or works that allow you to make modifications or commercial uses.
If your use doesn't fall under one of the exceptions to an author's exclusive rights, and if the work you want to use isn't in the public domain or available under a license that permits the use you want to make, you'll have to request permission from the author or copyright holder.
First, you have to identify the copyright holder. Next, you should request permission in writing, specifying what it is you want to use and how you want to use it. You should also make sure that you get the permission of the copyright holder in writing so that it constitutes a legitimate license. If permission is granted, be sure to appropriately attribute the work. If you don't get permission, or if that permission comes at too high of a cost, you may have to change your proposed use or use another work.
For more detail on requesting permission, see the Copyright Office's guide to making permissions requests.