HTML5 Canvas to JPG: Generate Images with JavaScript

<p><canvas id='canvas'></canvas></p>
<script>
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var img = ctx.getImageData(0, 0, canvas.width, canvas.height);
var data = img.data;
for (var i = 0; i < data.length; i += 4) {
data[i] = 255;   // red
data[i + 1] = 0;   // green
data[i + 2] = 0;   // blue
}
ctx.putImageData(img, 0, 0);
var dataURL = canvas.toDataURL('image/jpeg');
</script>