The source code for the game the mtPlace server runs.
This is a game, like any other. Recursively clone this repository to your games folder, make a new singlenode world with this game and start up a Minetest server for it.
For the screenshotter, see screenshot.sh. It uses minetestmapper to take a top-down screenshot of the map, saves the image, runs optipng in it and symlinks it in such a way that the latest image is always available at /place.png in the website's root folder. This script should be run with a cronjob or something similar.