images = new Array('00.jpg', '01.jpg', '02.jpg', '03.jpg');
index = Math.floor(Math.random() * images.length);


var path = 'images/bgPics/';
var i, numImages = 10;

function randomChange() {
   var cell = document.getElementById('midimage');
   var randomIndex = Math.floor(Math.random() * numImages)+1;
   cell.style.backgroundImage = 'url(' + String(path + 'bgPic' + randomIndex + '.jpg') + ')';
   //alert(cell.style.backgroundImage);
}
window.onload = randomChange;