[fearmear.wrk]

Пример с Promise. JSFiddle

var canvas = document.createElement('canvas'); 
var context = canvas.getContext('2d');

function loadImage(src){
	return new Promise(function(resolve){
  	var pic = new Image();
    pic.onload = function(){
      canvas.width = pic.width;
      canvas.height = pic.height;
      resolve(pic);
    }
    pic.crossOrigin = 'anonymous';
    pic.src = src;
  });
}

function drawImage(pic){
  context.drawImage(pic, 0, 0, pic.width, pic.height);	
  context.fillStyle = "black";
  context.font = 'bold 30px sans-serif';
  context.fillText("Autor Famyly", 290, 235);
  return canvas.toDataURL("image/png");
}

function saveImage(dataURL) {
  var a = document.createElement('a');
  a.href = dataURL;
  a.download = 'Certificate';
	a.click();
};

loadImage('http://i.imgur.com/fHyEMsl.jpg').then(drawImage).then(saveImage);