Prior to Performance Timeline API getting list of all images in document would require looking at document.images and inspectomg stylesheets to find any referenced background-images; but now with the Performance Timeline API it's easy to get a list of all images (assuming they have image filename extensions)

list-document-images.js

function getDocumentImages() {
  return performance.getEntriesByType('resource')
    .map( ( entry ) => entry.name )
    .filter( ( url ) => { 
      const parsedUrl = new URL( url ); 
      return /\.(png|jpe?g|gif|webp|svg)$/i.test( parsedUrl.pathname ); 
  } );
}