snapshot.js

var takeSnapshot = function() {
    // A function to take a snapshot
    var canvas = document.querySelector('canvas'); // Grab the canvas
    var image = canvas.toDataURL("image/png").replace("image/png", "image/octet-stream"); // Save the image
    setTimeout(function() { window.location.href=image; }, 100); // Wait a bit to download the image; probably should use an event listener instead
}

// Regularly take a snapshot every 200ms
var timer = setInterval(takeSnapshot, 200)