Useful

convertImagesToBase64.js

  function convertImagesToBase64 () {
      contentDocument = tinymce.get('content').getDoc();
      var regularImages = contentDocument.querySelectorAll("img");
      var canvas = document.createElement('canvas');
      var ctx = canvas.getContext('2d');
      [].forEach.call(regularImages, function (imgElement) {
        // preparing canvas for drawing
        ctx.clearRect(0, 0, canvas.width, canvas.height);
        canvas.width = imgElement.width;
        canvas.height = imgElement.height;
        ctx.drawImage(imgElement, 0, 0);
        // by default toDataURL() produces png image, but you can also export to jpeg
        // checkout function's documentation for more details
        var dataURL = canvas.toDataURL();
        imgElement.setAttribute('src', dataURL);
      })
      canvas.remove();
    }