this is mod for Secure Shell(Google Chrome Extension).

yuyusshiki.js

var xhr = new XMLHttpRequest();
var url = 'https://gist.github.com/tyage/7823731/raw/b1ff47d4444f68fe76b3e91423648bb4d58eb564/yuyulist';
xhr.open('GET', url, true);
xhr.onloadend = function onReady() {
  if (xhr.readyState != XMLHttpRequest.DONE || xhr.status != 200)
    return;

  var images = this.responseText.split("\n");
  var screen = document.querySelector("#terminal>iframe").contentDocument.querySelector("x-screen");
  screen.style.setProperty('background-size', '100%', '!important');
  screen.style.setProperty('background-repeat', 'no-repeat', '!important');
  var changeBackground = function() {
    var image = images[Math.floor(Math.random() * images.length)];
    screen.style.setProperty('background-image', 'url("' + image + '")', '!important');
  };
  changeBackground();
  setInterval(changeBackground, 1000*10);

  // deny default settings
  hterm.ScrollPort.prototype.setBackgroundImage = function() {};
  hterm.ScrollPort.prototype.setBackgroundSize = function() {};
};
xhr.send();