Image functionality ported from pdf.js
function createDataURIFromElement(element, format) {
    //if element is an image which uses data url definition, just return the dataurl
    if (element.nodeName === 'IMG' && element.hasAttribute('src')) {
      var src = '' + element.getAttribute('src'); //is base64 encoded dataUrl, directly process it

      if (src.indexOf('data:image/') === 0) {
        return unescape(src);
      } //it is probably an url, try to load it


      var tmpImageData = jsPDFAPI.loadFile(src);

      if (tmpImageData !== undefined) {
        return btoa(tmpImageData);
      }
    }

    if (element.nodeName === 'CANVAS') {
      var canvas = element;
      return element.toDataURL('image/jpeg', 1.0);
    } //absolute fallback method


    var canvas = document.createElement('canvas');
    canvas.width = element.clientWidth || element.width;
    canvas.height = element.clientHeight || element.height;
    var ctx = canvas.getContext('2d');

    if (!ctx) {
      throw 'addImage requires canvas to be supported by browser.';
    }

    ctx.drawImage(element, 0, 0, canvas.width, canvas.height);
    return canvas.toDataURL(('' + format).toLowerCase() == 'png' ? 'image/png' : 'image/jpeg');
  }