title: How to merge a canvas created by Konva on a blob:http image so it can be sent in an email
body: <p>I would really appreciate any help I could get with this. I am stoke for hours now. I am trying to do a webApp Function where people can take a selfie, then put an image over it and send it to an e-mail.
  Till now I have this:</p>
  
  <pre><code>&lt;img id="frame"&gt;
  &lt;script type="text/javascript"&gt;
      var camera = document.getElementById('camera');
      var frame = document.getElementById('frame');
      camera.addEventListener('change', function(e) {
          var file = e.target.files[0];
          // Do something with the image file.
          frame.src = URL.createObjectURL(file);
          alert(frame.src);
      });
  &lt;/script&gt;
  &lt;div id="container"&gt;&lt;/div&gt;
  &lt;script type="text/javascript"&gt;
      var width = window.innerWidth;
      var height = window.innerHeight;
  
      function drawImage(imageObj) {
          var stage = new Konva.Stage({
              container: 'container',
              width: 800,
              height: 400,
          });
          var layer = new Konva.Layer();
          // darth vader
          var darthVaderImg = new Konva.Image({
              image: imageObj,
              x: stage.getWidth() / 2 - 200 / 2,
              y: stage.getHeight() / 2 - 137 / 2,
              width: 200,
              height: 137,
              draggable: true
          });
          // add cursor styling
          darthVaderImg.on('mouseover', function() {
              document.body.style.cursor = 'pointer';
          });
          darthVaderImg.on('mouseout', function() {
              document.body.style.cursor = 'default';
          });
          layer.add(darthVaderImg);
          stage.add(layer);
      }
      var imageObj = new Image();
      imageObj.onload = function() {
          drawImage(this);
      };
      imageObj.src = 'kochmuetze.png';
  &lt;/script&gt;
  </code></pre>
  
  <p>It takes the picture and I can drag the <em>kochmuetze.png</em> on the image. But how to I save the combination to one image?</p>