Why can't I use just any image I find online? In a word, copyright! The creator of any image has the exclusive legal right to use, share, or adapt images.
If you want to use the image yourself, you generally need to get permission from the rights owner OR be able to justify yourself under Fair Use guidelines. If you use images for school (in a PowerPoint, for example), then you're okay because you are using the image for educational purposes. BUT if you are looking to make money from using an image (in an advertisement, for example), then you are leaving yourself open to a cease-and-desist order or lawsuit.
Generally you should try to use images whose creators released them to the world under a Creative Commons license (see below).
Creative Commons (CC) frees up creative works from the bulk of copyright restrictions. CC-licensed works often can be used, shared, or adapted freely for educational purposes, as long as you cite the creator. Watch for the CC logo!
A CC license example is below.
This work is licensed under a Creative Commons Attribution 4.0 International License
Google Images narrows your Google search to images. From the search results page, click on Images. Then you can click on "Tools" (just below the main search box) and narrow your results by "Usage Rights." NOTE: Check the source to verify that the image is free to use.
CC Search: A one-page federated search. Creative Commons offers this shortcut to searching Flickr, Open Clip Art, Wikimedia, and other major image commons. If you are looking for free online images to use with few restrictions, look no farther!
Flickr Creative Commons enables you to search over 200 million photos shared by regular users for that one free, open, CC-licensed image that's just right for you.
Wikimedia Commons offers over 24 million free photos and other media files to which anyone can contribute. Everything is distributed under Creative Commons licenses or is in the public domain. Check out the photo challenges too. This is the Wikipedia of pictures!
Need more sources for images? 85 Free Stock Photo Resources- How to Use Them (CC licenses)
ClipArt Etc offers more than 66,000 quality educational clipart distributed under an open license by the University of South Florida.
Pixabay offers over 100,000 photos, vectors, and illustrations free and with zero copyright restrictions on how you can use them.
Always give credit where credit is due! When you use images in a PowerPoint or webpage, be sure to cite your sources.
In your citation, include the name of service (Flickr, Getty, etc.), the name or username of the person who created the image, and the image's URL.
Place the citation in small font just below the image. Here is an example. Credit: Flickr user Kenny Teo, https://flic.kr/p/n8gNQC
Generally you should not include images on your References page. Please check with your instructor if you have any questions about properly citing images.