title: Can't download canvas content
body: <p>So Im trying to build an app using electron, the program is pretty basic, the user should upload a couple of pictures, they press a button, I draw them into a <code>&lt;canvas&gt;</code> element and they should be able to download it, the problem that Im having is that when I try to make a downloadable button, a security error is thrown, I did some research and find out that it's a feature of HTML5, the think is that i can't add the crossOrigin = 'Anonymous' because the user is going to load the picture from its own computer, so my question is... </p>
  
  <p>a)- is there a way to "cheat the system" and be able to download the content of the canvas?,</p>
  
  <p>b)- if (a) is not posible...is there an alternative that could work similary to a canvas element? </p>
  
  <p>I'm already using FileReader() to get the picture the user selected, and i'm already drawing that into the canvas, and it looks great, the problem that I have is that i can't download the content that I created for that security error. the .toDataURL can't be called because that's the one that throws the error.</p>
  
  <p>The code to read the pictures from the inputs:</p>
  
  <pre><code> function handleBox1(evt) {
      var files = evt.target.files; // FileList object
  
      for (var i = 0, f; f = files[i]; i++) {
        // Only process image files.
        if (!f.type.match('image.*')) {
          continue;
        }
        var reader = new FileReader();
  
        reader.onload = (function(theFile) {
          return function(e) {
  
              $('#imgBox1').attr("src",e.target.result);              
  
          };
        })(f);
        // Read in the image file as a data URL.
        reader.readAsDataURL(f);
      }
  }
  </code></pre>
  
  <p>this is a simple function to see if I could get the Url from the canvas:</p>
  
  <pre><code>descargar = function(){
    var w=window.open('about:blank','image from canvas');
    w.document.write("&lt;img src='"+ totem.toDataURL("image/png")+ "' alt='from canvas'/&gt;");
  }
  </code></pre>