function show(imageId){

   document.getElementById(imageId).style.display = "block";
   document.getElementById(imageId).style.opacity = "1";
   document.getElementById(imageId).style.MozOpacity = "1";
   document.getElementById(imageId).style.filter = "alpha(opacity=100)";
    
   
   document.getElementById("img_main").style.display = "none";
   document.getElementById("img_main").style.opacity = "0";
   document.getElementById("img_main").style.MozOpacity = "0";
   document.getElementById("img_main").style.filter = "alpha(opacity=0)";
}

function hide(imageId){
   
   document.getElementById(imageId).style.display = "none";
   document.getElementById(imageId).style.opacity = "0";
   document.getElementById(imageId).style.MozOpacity = "0";
   document.getElementById(imageId).style.filter = "alpha(opacity=0)";
   
   
   document.getElementById("img_main").style.display = "block";
   document.getElementById("img_main").style.opacity = "1";
   document.getElementById("img_main").style.MozOpacity = "1";
   document.getElementById("img_main").style.filter = "alpha(opacity=100)";
}