The digitized reproductions of the Calvin and Hobbes comics are technically violating copyright law unless financial compensation was given to the creator of the image, Bill Watterson. The comic strip would also not violate copyright law if the image was obtained legally and used for only non-profit face to face education according to the copyright law on educational materials. By saying the material was obtained legally means that the image was copied from a library, official archive, or purchased legally. Any copy that came from the internet, television or radio, or duplicated from a colleague’s copy is illegal.
Therefore, if the comic strip that is posted on the syallbus does not violate copyright law if the image was legally acquired by one of the methods posted above, because it is used for educational purposes. The placement of the image would also be illegal if it was placed on the site without an purpose other than to entertain; that is somewhat true in this case but cannot really be argued for because the image teaches a lesson related to the class. If the image appeared on any other website that was not directly connected to an official class and was not legally purchased from the creator, then it would be a case of copyright infringement.