.bg {
  background: url('../images/bg.jpg') no-repeat center center;
  position: fixed;
  width: 100%;
  height: 450px; /*same height as jumbotron */
  top:0;
  left:0;
  z-index: -1;
}

.jumbotron {
  height: 450px;
  color: white;
  text-shadow: #444 0 1px 1px;
  background:transparent;
  top:0;
}