function  showImage(){
    document.getElementById("imgPlace").src=aUrl + aImage[aImage.Index][0];
	document.getElementById("caption").innerHTML = aImage[aImage.Index][1];
	if (aImage.Index==aImage.length-1) 
	{
		document.getElementById("forth").style.visibility = 'hidden';
	} 
	if (aImage.Index==0)
	{
		document.getElementById("back").style.visibility = 'hidden';
	}
}

function forth_onclick() {
	if (aImage.Index+1==aImage.length) return;	
	document.getElementById("back").style.visibility = 'visible';
	document.getElementById("imgPlace").src="images/loading.gif";
	aImage.Index++;
	showImage();
}

function back_onclick() {
	if (aImage.Index==0) return;
	document.getElementById("forth").style.visibility = 'visible';
	document.getElementById("imgPlace").src="images/loading.gif";
	aImage.Index--;
	showImage();
}