var inum = 1;
ImgNormal = new Image();
ImgNormal.src = "/images/rot_image.jpg";
ImgLines = new Image();
ImgLines.src = "/images/rot_lines.jpg";

function nextimage()
{
  var imag = document.getElementById("rotimage");
  inum = inum + 1;
  if (inum>1) {
    imag.src = ImgNormal.src;
    inum = 0;
  } else {
    imag.src = ImgLines.src;
  }
  setTimeout("nextimage()", 4000)
}