I wouldn't expect to find too many images of the actual liturgy itself, but
there is lots of online material about fools:

This site is dedicated to recreating the fool's costume, but has the
references to medieval and renaissance illustrations.

Beatrice Otto's book Fools Are Everywhere published by U. of Chicago
includes a website with links.

Otto's own website is called

In the ORB, Michael George writes about Laughter in the Middle Ages

This site is devoted to the mythic archetype of the Trickster, some

A fun subject to be working with

Amelia Carr