hide_image.user.js

// ==UserScript==
// @name        hideImages
// @namespace   hideImages
// @description hideImages
// @version     1
// @grant       none
// ==/UserScript==
var pic = 'http://i.imgur.com/BkygUho.png';
var a = '-1';
while (a < document.images.length) {
  a++;
  if(document.images[a]!==undefined)
  document.images[a].src = pic;
}

$('iframe').each(function () {
  $(this).replaceWith('<img src="http://i.imgur.com/BkygUho.png">');
});