gistfile1

var o = "", bd = document.body, h = bd.innerHTML;
h += h;h += h;h += h;

console.time(1);
h.replace(
        /(?:<img[^>]*?)(?:src *?= *?("[^"]+"|'[^']+'|[^ >]+))/ig,
        function(m, src) {
            src = src.replace(/^['"]/,'').replace(/['"]$/,'');
            o += "<li>" + src + ' <img src="' + src + '" /></li>';
        });
console.timeEnd(1);

console.time(4);
t=h.match(/(?:<img[^>]*?)(?:src *?= *?("[^"]+"|'[^']+'|[^ >]+))/ig)
console.timeEnd(4);

o = "";
console.time(2);
h.replace(
        /(<img[^>]*)(src *= *("[^"]*"|'[^']*'|[^ >]*))/ig,
        function(m, t, c, src) {
            t = src; c = src.charAt(0);
            if (c == '"' || c == "'") t = t.slice(1, -1);
            o += "<li>" + t + " <img src=" + src + " /></li>";
        });
console.timeEnd(2);

o = "";

console.time(3);
o = h.replace(
  /^.*?(?:<img[^>]*?)(?:src *?= *?("[^"]+"|'[^']+'|[^ >]+))/img,
  '<li>$1<img src="$1"/></li>');
console.timeEnd(3);