Combined result of images exported from canvas

by Thomas B.

HTML

<p>Source images</p>
        <div id="sources">
            <img id="front" src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/window.png" width=150 height=105>
            <img id="middle" src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/person.png" width=48 height=133>
            <img id="back" src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/SPback.png" width=150 height=105><br>
        </div>
        <p>Combined result exported from canvas</p>
        <p>To Save: Right-click and Save picture as...</p>
        <img id="composition">

CSS

body {
            background-color: ivory;
            padding:15px;
        }
        canvas {
            border:1px solid red;
        }
        #sources {
            border:5px solid blue;
            padding:15px;
            width:380px;
        }
        p {
            margin:15px 0;
        }

JavaScript

var back = new Image();
        back.onload = function () {
            draw();
        }
        back.crossOrigin = "Anonymous";
        back.src = "https://dl.dropboxusercontent.com/u/139992952/stackoverflow/SPback.png";

        var person = new Image();
        person.onload = function () {
            draw();
        }
        person.crossOrigin = "Anonymous";
        person.src = "https://dl.dropboxusercontent.com/u/139992952/stackoverflow/person.png";

        var awindow = new Image();
        awindow.onload = function () {
            draw();
        }
        awindow.crossOrigin = "Anonymous";
        awindow.src = "https://dl.dropboxusercontent.com/u/139992952/stackoverflow/window.png";

        var count = 0;

        function draw() {
            count++;
            if (count < 3) {
                return;
            }

            var canvas = document.createElement("canvas");
            var ctx = canvas.getContext("2d");
            canvas.width = awindow.width;
            canvas.height = awindow.height;

            ctx.drawImage(back, 0, 65);
            ctx.drawImage(person, 0, 0, person.width, person.height, 200, 125, 71, 200);
            ctx.drawImage(awindow, 0, 0);
            var result = document.getElementById("composition");
            result.src = canvas.toDataURL();
        }