Including cartoons in lecture notes?

As an undergraduate, I always appreciated when profs did stuff like this. It made it look like they actually put some effort into their notes, and a laugh was always appreciated in the middle of a frustrating and hard lecture.

xkcd is fine if you respect their license, Creative Commons Attribution-NonCommercial 2.5. phdcomics are likely fine, as they come from the broader academic-nerd community, but it's always worth doing some research first (google for the name of the cartoon you're copying + "DMCA" or "takedown" for example). Dilbert? No idea. I don't think a fully included comic would necessarily fall under fair use.

There are some minor disadvantages, though:

• You cannot release your notes under a more permissive license than the one your sources come with.

• The size of your file is inflated, along with the compile time perhaps (assuming LaTeX).

• As a consequence of both preceding points, it makes it harder to archive your notes for the long term (e.g., on arXiv or zenodo or even the AMS Open Math Notes repository). Doubly so if the comic strips get a new "owner" who starts using them as a copyright cudgel.

• Not all students will like or even understand the joke. This holds particularly when a long-running comic strip accumulates inside lore, caters to a specific audience or follows a cryptic style (e.g. C&H).