var head_img_url="";

(function(){
	var img= new Image();
	head_img_url = 'http://earth1.jp/images/top' + Math.floor(Math.random()*12) + '.jpg';
	img.src= head_img_url;
	document.write("<style>#head_image{visibility:hidden}<\/style>");		  
})()

function changeImage(){
	document.getElementById("head_image").innerHTML="<img src='"+head_img_url+"' alt='Earth One Office' with='640' height='195' />";	
	document.getElementById("head_image").style.visibility="visible";
}