function ReplaceBG(thumbnails) {
	var picsource = thumbnails.replace("gif","jpg");
	var cssvalue = "url("+picsource+")";
	var allbox = document.getElementById("allbox");
	allbox.style.backgroundImage = cssvalue;
}
var ReplaceBGlist = document.getElementById("ReplaceBG").getElementsByTagName("img");
for (i=0; i<ReplaceBGlist.length; i++) {
	ReplaceBGlist[i].onclick = function() {
		ReplaceBG(this.src);
	}
}