images = new Array(4);
images[0] = "<img src='images/masthead_industry_01.jpg' width='705' height='136'>";
images[1] = "<img src='images/masthead_industry_02.jpg' width='705' height='136'>";
images[2] = "<img src='images/masthead_industry_03.jpg' width='705' height='136'>";
images[3] = "<img src='images/masthead_industry_04.jpg' width='705' height='136'>";

index = Math.floor(Math.random() * images.length);

document.write(images[index]);