html5: how to handle canvas child clicked event?

<canvas id="myCanvas" width="578" height="400"></canvas>
<script>
  var canvas = document.getElementById('myCanvas');
  var context = canvas.getContext('2d');
  var imageObj = new Image();
  imageObj.onload = function() {
    context.drawImage(imageObj, 128, 128);
  };
  imageObj.src = 'http://xxx/yyy/zzz.jpg';
</script>

How can I get notified or hooked with an event handler, when the imageObj, the child of the canvas object (not the canvas) is clicked?