twisangi.user.js

// ==UserScript==
// @name           twittersangokushi.googleimage
// @namespace      http://fuba.moaningnerds.org/
// @include        http://ninth.jp/twitter/app/sangoku.php?id=*
// @version        0.2
// ==/UserScript==

// This code is stolen from http://www.kagami.org/wikipedia_googleimage/wikipedia_googleimage-0.2.user.js

(function () {
    var searchbase = 'http://images.google.co.jp/images?hl=ja&oe=UTF-8&ie=UTF-8&um=1&q=';
    var apibase = 'http://ajax.googleapis.com/ajax/services/search/images?v=1.0&q=';
    var word = document.getElementsByTagName('b')[1].innerHTML;
    var searchurl = searchbase + word;
    var apiurl = apibase + word;

    var img = document.createElement('img');
    img.alt = 'Google Image Search: ' + word;

    var a = document.createElement('a');
    a.appendChild(img);
    a.href = searchurl;

    var p = document.createElement('p');
    p.appendChild(a);

    var txt = document.getElementsByTagName('p')[0];
    txt.parentNode.insertBefore(p, txt.nextSibling);

    GM_xmlhttpRequest({
        method: 'GET',
	url: apiurl,
        headers: { 'User-agent': 'Mozilla/4.0 (compatible) Greasemonkey' },
	onload: function(responseDetails) {
	    var res = eval('(' + responseDetails.responseText + ')'); 
	    img.src = res.responseData.results[0].tbUrl;
	}
    });
})();

What exactly does this script do?