window.onload = choosePic;

var myPix = new Array("site_pics/header_changePic1.png","site_pics/header_changePic2.png","site_pics/header_changePic3.png","site_pics/header_changePic4.png");

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