var photo = new Image();

function preload() {
	for (var img in document.images) {
		photo.src = document.images[img].src;
		}
	}

function mouse_over(id_element) {
	var baseUrl = 'http://www.lesrivesdavalon.com/';
	document.getElementById('thumb').src = baseUrl + document.getElementById(id_element).getAttribute('imgsrc');
	}