Dump background-image property from every element on a page

dump-background-images.js

function getBackgroundUrl(bg) {
  var match = bg.match(/url\(["']([^'"]+)['"]\)/);
  if (match && match.length == 2) { return match[1]; }
  return null;
}

backgroundUrls = new Set();
document.querySelectorAll('*')
  .forEach(function(el) {
    var background = el.style.background || window.getComputedStyle(el).background;
    if (!background) {
      return;
    }
    var backgroundUrl = getBackgroundUrl(background);
    if (!backgroundUrl) {
      return;
    }
    backgroundUrls.add(backgroundUrl);
  });

Array.from(backgroundUrls)