Did you know you can reverse look-up images in Google? This can be helpful when trying to find sources that your students used for images and content related to the images, among other things. Reverse look-up results include information on where else the image is being used online, a list of visually similar images, and pages that include matching images.
Save the image to your computer. Then drag it to the search box at images.google.com.
More detailed instructions: https://support.google.com/websearch/answer/1325808?hl=en