function emailPage() {
  var messageText = 'Hello, I found a great web page at ' + window.location;
  var subjectText = 'Check out this Website';
  var email = prompt("Enter your friend's email address:", '');
  if ( (email == "") || (email == null) ) {
      alert("You need to enter an e-mail address");
      emailPage();
  } else {
    window.location = 'mailto:' + email +
      '?subject=' + encodeURIComponent(subjectText) +
      '&body=' + encodeURIComponent(messageText);
  }
}

function swap_images(id,url)
{
	document.getElementById(id).src = url;
}