NumberOfImagesToRotate = 4;

// Specify the first and last part of the image tag. 

FirstPart = '<img class="strapline" src="/Portals/0/Skins/VDS/Images/Branding/strapline';
LastPart = '.gif" height="20" width="380">';

function printImage() {
var r = Math.ceil(Math.random() * NumberOfImagesToRotate);
document.write(FirstPart + r + LastPart);
}