Edit in JSFiddle

var imagenes = document.getElementsByTagName("img"),
    labels = document.getElementsByTagName("label"),
    totalImg = imagenes.length;

for (i = 0; i < totalImg; i++){
    var src = imagenes[i].src;
    labels[i].innerHTML = src.substring(src.lastIndexOf("/") + 1, src.lastIndexOf("."));
}