.bg-img {
  position: absolute;
  width: 100%;
  height: 100%;
  background: url(http://www.reactiongifs.us/wp-content/uploads/2015/04/nothing_to_see_here_naked_gun.gif) no-repeat center center fixed;
  background-size: cover;
  background-color: #000;
  opacity: .5;
  filter: alpha(opacity=50);
}