How do I use potentially copyrighted images in my course material?
Images found in Google search don't belong to Google.

I can't speak to fair-use under academia, but I can say images aren't fair game just because they're found on Google images

There are, however, places you can find images you can use. Wikimedia has a ton of images that can be used, with a wide variety of licenses for re-use. Flickr is another that comes to mind.

I want to reiterate that I don't know fair use under the realm of academia, but would ask permission and highly recommend captioning photos in order to give credit where it's due.