imageshack.user.js

// ==UserScript==
// @name        ImageShack one-click recovery
// @version     0.2
// @namespace   http://vyznev.net
// @description Highlights ImageShack images on Stack Exchange, and adds a click hadler that attempts to reload them from archive.org
// @author      Ilmari Karonen
// @license     ISC (http://opensource.org/licenses/ISC)
// @match       *://*.stackexchange.com/*
// @match       *://*.stackoverflow.com/*
// @match       *://*.superuser.com/*
// @match       *://*.serverfault.com/*
// @match       *://*.stackapps.com/*
// @match       *://*.mathoverflow.net/*
// @match       *://*.askubuntu.com/*
// @grant       none
// ==/UserScript==

var inject = function ($) {
  var re = /^https?:\/\/(([\-a-z0-9]+\.)*imageshack\.us\/img\d+\/.*)$/i;
  $(document).on('click', 'img[src*="imageshack.us"]', function () {
    var m = re.exec( this.src );
    if (!m) return true;
    this.src = "http://web.archive.org/web/2/" + m[1];
    return false;
  } );
};

var script = document.createElement('script');
script.textContent = "(" + inject + ")(jQuery);";
(document.body || document.documentElement).appendChild(script);

var style = document.createElement('style');
style.textContent = 'img[src*="imageshack.us"] { opacity: 0.33; border: 2px dashed red; }';
(document.head || document.documentElement).appendChild(style);