The mob head datapack the Minetown Server uses. The datapack is a modified version of VanillaTweaks and the rights on all image files belong to them. This combines the player head drops module with the more mob heads module and adds a random chance to the player head drops. You can find a list of all available heads here.
This step should be automatically performed by a GitHub action. To do it manually, follow the instructions below. The scripts for this project are written in python and the required dependencies can be found in requirements.txt. To regenerate the head overview, you need to execute the following command:
python3 scripts/generate_head_overview.py