var currentImage = 1;
  var id_prefix = "#product-image-";

  function switchImage ( newImage )
  {
    if (newImage == currentImage)
    {
      return false;
    }

    $(id_prefix + currentImage).attr( "class", "image_hidden");
    $(id_prefix + newImage).removeAttr( "class" );
    currentImage = newImage;
  }