http://d.hatena.ne.jp/mallowlabs/20061012/1160662103

googleimagefilter.user.js

// ==UserScript==
// @name googleimagefilter
// @author mallowlabs
// @namespace http://mallowlabs.s206.xrea.com/
// @version 0.0.2
// @license public domain
// @description : Add a switch that on/off the filter in Google Image Search
// @published 2006-11-12
// @modified 2007-07-16
// @include http://images.google.co.jp/*
// ==/UserScript==
//
// ChangeLog
//  2007-07-16 0.0.2 fix broken layout.
//  2006-11-12 0.0.1 released.
//
// =========================================
// =========================================
(function () {

	var tableNode = document.getElementsByTagName("table")[3];
	var trNode = tableNode.getElementsByTagName("tr")[0];
	
	var tdNode = document.createElement("td");
	tdNode.setAttribute("nowrap", "");

	if(!isFiltering()){
		aNode = createANode("safe=images", "FilterON");	
	}else{
		aNode = createANode("safe=off", "FilterOFF");
	}

	tdNode.appendChild(aNode);
	trNode.appendChild(tdNode);
	
	function isFiltering(){
		var aNodes = document.getElementsByTagName("a");
		for (var i = 0; i < aNodes.length; i++) {
			if ( aNodes[i].getAttribute("href").search(/^\/preferences/) != -1 ) {
				break;
			}
		}
		
		var strCheckUrl = aNodes[i].getAttribute("href");
		var param = strCheckUrl.slice(strCheckUrl.indexOf("?")+1).split("&");
		var mode = true;
		for (var i = 0;i < param.length; i++) {
			if (param[i]=="safe=off"){
				mode = false;
				break;
			}
		}
		return mode;
	}
	
	function createANode(newsafe, newtext){
		var ref = location.href.slice(0, location.href.indexOf("?")+1);
		var param = location.href.slice(location.href.indexOf("?")+1).split("&");
		for (var i = 0;i < param.length; i++) {
			if (param[i].search(/safe=/) != -1) {
				ref += newsafe + "&";
			}else{
				ref += param[i] + "&";
			}
		}
		ref = ref.slice(0, ref.length - 1);
		if(ref.search(/&safe=/) == -1){
			ref += "&" + newsafe;
		}
		var textNode = document.createTextNode(newtext);
		var aNode = document.createElement("a");
		aNode.setAttribute("href", ref);
		aNode.appendChild(textNode);
		return aNode;
	}

})();