img = new Array();
alt = new Array();

img[0] = "img/emain_img_a.jpg";
img[1] = "img/emain_img_b.jpg";
img[2] = "img/emain_img_c.jpg";

alt[0] = "GENERAL BUIDLING RESEARCH CORPORATION OF JAPAN";
alt[1] = "GENERAL BUIDLING RESEARCH CORPORATION OF JAPAN";
alt[2] = "GENERAL BUIDLING RESEARCH CORPORATION OF JAPAN";

n = Math.floor(Math.random()*img.length);

document.write("<img src='"+img[n]+"' border='0' alt='"+alt[n]+"'>");