click on the poster/album cover for the large version. they're not always available.
// ==UserScript==
// @name itunes - get large artwork
// @namespace KG
// @include http*://itunes.apple.com/*/movie/*
// @include http*://itunes.apple.com/*/album/*
// @grant none
// @version 0.3
// @description click on the poster/album cover for the large version. they're not always available.
// ==/UserScript==
var poster = document.getElementById('left-stack').getElementsByTagName('img')[0];
// movies
var big = poster.src.replace(".227x227-75", "");
// albums/singles
big = big.replace(".170x170-75", "");
poster.setAttribute("onclick", "javascript: window.location.href=' " + big + " '; return false;");