All Public Domain and Creative Commons images can be saved to your computer and reused in your own work, whether it is a PowerPoint, blog, wiki or other instance. It is always best practice to reference your images even if they are in the Public Domain. You can also hyperlink your image to its source page. See Best practices for attribution for tips on referencing your images. Carleton University also have a great guide for citing a screenshot.
Below is an example of good attribution or referencing of an image from Wikimedia Commons which was captured with Snipping Tool and reused here. Note that text and image are hyperlinked to the source page.
1. Click Insert in the top ribbon
2. Click Online Pictures
3. Search for an image
4. Keep Creative Commons Only ticked
5. Click the image and choose Insert
6. Your image shows with hyperlinks to the source and the Creative Commons Licence below it.
Other Public Domain Image Sources
Remember since you are working in an academic environment referencing will ALWAYS be required. Referencing means you are covered in relation to copyright and plagiarism by acknowledging the resource is not yours and it also helps you or someone else find it again if required. For more information on copyright and referencing have a look at the above tab called APA Referencing
Everyone tends to "Google" images. To avoid copyright breaches, follow this process:
1) Search in Google images
2) Click on Tools
3) Click on Usage Rights
4) Select Labeled for reuse - these images are usually from the Public Domain or Creative Commons.
YouTube Videos can only be downloaded if they have a Creative Commons license. To find CC videos, click the “Filter” tab at top left and look for the “Creative commons” option, or use CC Search. To view licence details for a video, click the "Share" button, then look for "SHOW MORE". Some also allow remixing and will link to a video editor.
Academic Earth Free educational videos from the world's top universities.
TED-Ed Educational videos created by TedEd collaborators or by teachers who have added supplementary content to YouTube videos.
Videezy Free background video footage, mostly scenic.