// Type the number of images you are rotating.

NumberOfImagesToRotate = 3;

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

FirstPart = '<img src="http://www.endodonticcenter.com/images/header_';
LastPart = '.jpg" height="134" width="631">';

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