function replaceWithPressedImage(image_id)
  {
  document.getElementById(image_id).src="images/add_to_cart_pressed.gif";
  }
function replaceWithReleasedImage(image_id)
  {
  document.getElementById(image_id).src="images/add_to_cart.gif";
  }
function replaceWithPressedImageWC(image_id)
  {
  document.getElementById(image_id).src="images/view_cart_pressed.gif";
  }
function replaceWithReleasedImageWC(image_id)
  {
  document.getElementById(image_id).src="images/view_cart.gif";
  }