Gastei um bocado da minha matematica da 5 serie porque coloquei o quadrado verde no centro do canvas ^^
<canvas width="600" height="400"></canvas>
<script>
var myScreen = document.querySelector("canvas");
var myBlush = myScreen.getContext("2d");
//green head centred
myBlush.fillStyle = "darkgreen";
myBlush.fillRect(125, 50, 350, 300);
//left moustache
myBlush.fillStyle = "black";
myBlush.fillRect(225, 240, 40, 110);
//right moustache
myBlush.fillStyle = "black";
myBlush.fillRect(335, 240, 40, 110);
//nose
myBlush.fillStyle = "black";
myBlush.fillRect(265, 200, 70, 100);
//right eye
myBlush.fillStyle = "black";
myBlush.fillRect(335, 110, 90, 90);
//left eye
myBlush.fillStyle = "black";
myBlush.fillRect(175, 110, 90, 90);
</script>