function addLoadEvent(func) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {
      oldonload();
      func();
    }
  }
}

function switchPhoto() {
	if (!document.getElementsByTagName) return false;
  	if (!document.getElementById) return false;
  	if (!document.getElementById("nutezien")) return false;
	var plekje = document.getElementById("nutezien");
	var deLinks = plekje.getElementsByTagName("a");
	var eersteLink = deLinks[0];
	var linkAdres = eersteLink.getAttribute("href");
	var foto1 = document.getElementById("pieterfoto");
	eersteLink.onclick = function() {
		foto1.setAttribute("src",linkAdres);
		if (linkAdres == "http://www.pieterathmer.nl/images/pieter1.jpg" || linkAdres == "images/pieter1.jpg") {
			linkAdres = "http://www.pieterathmer.nl/images/pieter2.jpg";
			eersteLink.setAttribute("href","http://www.pieterathmer.nl/images/pieter2.jpg");
		}
		else if (linkAdres == "http://www.pieterathmer.nl/images/pieter2.jpg" || linkAdres == "images/pieter2.jpg") {
			linkAdres = "http://www.pieterathmer.nl/images/pieter1.jpg";
			eersteLink.setAttribute("href","http://www.pieterathmer.nl/images/pieter1.jpg");
		}
		return false;
	}
}

addLoadEvent(switchPhoto);