var logo;
window.onload = init;

function switchOn(){
  logo.width = 260;
  logo.height = 600;
  logo.src = "img/logo2.jpg";
}

function switchOff(){
  logo.width = 260;
  logo.height = 600;
  logo.src = "img/logo1.jpg";
}

function init() {
    logo=document.getElementById("logo");
    logo.onmouseover= switchOn;
    logo.onmouseout= switchOff;
}