var imgURL = ["sak_img/headpic01.png", "sak_img/headpic02.png", "sak_img/headpic03.png", "sak_img/headpic04.png", "sak_img/headpic05.png", "sak_img/headpic06.png"];
var n = Math.floor(Math.random() * imgURL.length);
document.write('<img src="'+imgURL[n]+'" width="305" height="100" alt="">');