MyImages=new Array();
MyImages[0]='/images/mainImage2.jpg';
MyImages[1]='/images/mainImage4.jpg';
MyImages[2]='/images/mainImage5.jpg';
MyImages[3]='/images/mainImage6.jpg';
function newImage()
{
document.getElementById("header-image").setAttribute("src", MyImages[Math.floor(Math.random()*4)])
}