Can you represent the arc of your course in four icons?
One of the best sources are the creative commons licensed ones from The Noun Project (just be sure to keep track of them so you can provide attribution). Save them to your computer and then combine into a single image using any available graphics software or a web tool like PhotoCollage. If you need a place to store your image, try the Storied Collector.
Inspired by the DS106 Four Icons / One Story Assignment
Example for "Course Arc in Four Icons":