Finding Images
Your professor can display copyrighted images in class because their use is covered by Section 110(1) of copyright law ("In Class Performances") which allows for the display of copyrighted images in a face-to-face teaching session. Your use is not covered by that act. However, you have other options for using images in your notes or for presentations.
Check out the Can I Use an Image? tool (based on Hirsh Library's image reuse tool) if you're wondering if you can reuse an image or if you need an image.
Find Images for Reuse
Images from Websites
Check the copyright policy of any webpage that contains images you would like to use to see if they allow you to reuse the image. Keep your eye out for Creative Commons licenses (featured below) that signify that you can reuse an image if you cite it. Remember that websites aren't always trustworthy sources of information.