var theImages = new Array();

theImages[0] = 'http://www.ed.sc.edu/graphics/banner1.png';
theImages[1] = 'http://www.ed.sc.edu/graphics/banner2.png';
theImages[2] = 'http://www.ed.sc.edu/graphics/banner3.png';
theImages[3] = 'http://www.ed.sc.edu/graphics/banner4.png';
theImages[4] = 'http://www.ed.sc.edu/graphics/banner5.png';
theImages[5] = 'http://www.ed.sc.edu/graphics/banner6.png';
theImages[6] = 'http://www.ed.sc.edu/graphics/banner7.png';
theImages[7] = 'http://www.ed.sc.edu/graphics/banner8.png';
theImages[8] = 'http://www.ed.sc.edu/graphics/banner10.png';
theImages[9] = 'http://www.ed.sc.edu/graphics/banner11.png';
theImages[10] = 'http://www.ed.sc.edu/graphics/banner12.png';
theImages[11] = 'http://www.ed.sc.edu/graphics/banner13.png';

var j = 0;
var p = theImages.length;
var preBuffer = new Array();
for (i = 0; i < p; i++){
   preBuffer[i] = new Image();
   preBuffer[i].src = theImages[i];
}
var whichImage = Math.round(Math.random()*(p-1));

function showImage(){
    document.getElementById("picMain").style.background = "#ccc url(" + theImages[whichImage] + ") top left no-repeat";
}