// Function that return a number between 0 and "nums - 1"
function getRandom(nums)
{
var ranNum= Math.round(Math.random()*nums);
return ranNum;
}
 
// Tells us how many images we have available.
var numberOfImages    = 14;
var randomNumber        = getRandom(numberOfImages);

// Create an array to hold the names of all images.
var image = new Array(numberOfImages);
image[0]="rnd_pic_1.jpg";
image[1]="rnd_pic_2.jpg";
image[2]="rnd_pic_3.jpg";
image[3]="rnd_pic_4.jpg";
image[4]="rnd_pic_5.jpg";
image[5]="rnd_pic_6.jpg";
image[6]="rnd_pic_7.jpg";
image[7]="rnd_pic_8.jpg";
image[8]="rnd_pic_9.jpg";
image[9]="rnd_pic_10.jpg";
image[10]="rnd_pic_11.jpg";
image[11]="rnd_pic_12.jpg";
image[12]="rnd_pic_13.jpg";
image[13]="rnd_pic_14.jpg";
image[14]="rnd_pic_15.jpg";
 
// Write the img tag with a random image name.
document.write("<img src='http://www.bwitty.com/bgimages/" + image[randomNumber] + "' width=716 height=226 />");