var imageheight = 341;
var imagewidth = 629;
var imagewidthclip = 260;
var movesize = 1;
var speed = 50;

var sleft = 0;
var sright;
var stimer;
var sdir = 0;

function panImage(){
  if(sdir == 0){  
    if(sleft < imagewidth - (imageheight + movesize)){
      sleft += movesize;
    }
    else{
      sdir = 1;
    }
  }
  
  else if(sdir == 1){  
    if(sleft > movesize){
      sleft -= movesize;
    }
    else{
      sdir = 0;
    }
  }
  
  sright = sleft + imagewidthclip;

  document.getElementById("pan").style.left = -sleft;
  document.getElementById("pan").style.clip = "rect(0 " + sright + " " + imageheight + " " + sleft +")";

  stimer = setTimeout("panImage()",speed);
}