function convertImgToBase64(url, callback, outputFormat){
  var canvas = document.createElement('CANVAS'),
    ctx = canvas.getContext('2d'),
    img = new Image;
  img.crossOrigin = 'Anonymous';
  img.onload = function(){
    canvas.height = img.height;
    canvas.width = img.width;
    ctx.drawImage(img,0,0);
    var dataURL = canvas.toDataURL(outputFormat || 'image/png');
    callback.call(this, dataURL);
    canvas = null; 
  };
  img.src = url;
}


convertImgToBase64('http://bit.ly/18g0VNp', function(base64Img){
  // Base64DataURL
});