const getImages = (el, includeDuplicates = false) => {
  const images = [...el.getElementsByTagName('img')].map(img => img.getAttribute('src'));
  return includeDuplicates ? images : [...new Set(images)];
};

// Examples
getImages(document, true); // ['image1.jpg', 'image2.png', 'image1.png', '...']
getImages(document, false); // ['image1.jpg', 'image2.png', '...']