window.onload = choosePic;

var myPix = new Array(
"images/mainpic/pic1.jpg",
"images/mainpic/pic2.jpg",
"images/mainpic/pic3.jpg",
"images/mainpic/pic4.jpg",
"images/mainpic/pic5.jpg",
"images/mainpic/pic6.jpg",
"images/mainpic/pic7.jpg",
"images/mainpic/pic8.jpg");

function choosePic() {
	randomNum = Math.floor((Math.random() * myPix.length));
	document.getElementById("mainPicture").src = myPix[randomNum];
}