When a creative work (image, text, video, music, art) is "copyrighted" or "under copyright," it means that you cannot use it without the permission of the owner, except in cases of fair use (see box below). Often the owner of the creative work will want to be paid before you can use his/her material. Images are considered creative works, so many of them are under copyright. You can find the UNC Library's advice on copyright here.
Information on this page will tell you about cases when you can use copyrighted material without permission (fair use), and about how to find material that's not under copyright (public domain materials or materials that are under Creative Commons licenses).
If you are a student or instructor and are planning to use images for presentation in class, your image use will fall into this category. Fair use means that you can use a creative work, or a portion of that work, for teaching and learning purposes (it has other meanings too, but this is the one that will be pertinent to you here) without getting permission from the owner. That means that if you want to include an image that you find online in a classroom presentation or on a student worksheet, you can often do so without the artist or owner's permission even if that image is under copyright. Even in a fair use situation, however, you should still cite the creator/owner of the source and give appropriate credit.
Note that every fair use situation is different, and you should evaluate each one separately. For a good website on determining whether a particular use counts as fair use, you can see the Fair Use Evaluator here or look at the sites below. Also note that fair use does not apply to every educational situation. If an image is under copyright, you should NOT use it on your personal website or in a conference poster/presentation without permission from the artist or owner. If you create a conference poster for a class that you are planning on displaying outside of class, you should keep this in mind.
For more information on what kinds of uses are and are not Fair Use, click on the links below.
If something is the public domain, it means that it is not under copyright at all, and you can use it without permission of any kind. Usually a work will enter the public domain for one of two reasons: either because it was made by the government and was never under copyright to begin with, or because its copyright is expired. If an image is in the public domain, you do not have to attribute the creator, but it may be a good idea to note that the image is in the public domain. That way people will understand why you have been able to use it freely.
Creative Commons licenses are special licenses that artists and media owners can use as an alternative to copyright. People use them because they allows media creators or owners to give others broader rights to reuse and alter their work. If the person who owns the media puts it under Creative Commons license, he or she will customize a license based on a range of options for how other people will be allowed to use or change it, and how the owner or artist would like to be given credit.
For a written resource on the different kinds of Creative Commons licenses, see the UNC Library's breakdown here.
If a work is under a Creative Commons license, the creator/owner can choose to require those who use or reuse his/her work to attribute the creator or owner. In some cases, the licensor may also require that the user include a link to the terms of the original license, if he or she is using the item online. In most cases, the website where you find the image will have a way of copy/pasting attribution or the CC license automatically. To find out how to find this information on particular websites, go to the "Find Open Images" page on this guide.
Most images in this guide are under copyright unless otherwise noted. UNC pays license fees to make them available to you. Most can still be used for things like class presentations (which fall under Fair Use), but cannot be used in publications. Always check the licenses on each image before you use it in any context.
Most resources consider scholarly publication a commercial use and forbid it without special permissions.
However: A growing number of Museum & Art sources make an exception and allow free use of their images for scholarly books and journal articles:
See each site for information about limits and procedures.