Użyj `background-size: cover`
.baner {
background-image: url('http://www.margherita.pl/shared_assets/images/backgrounds/pizza/pizza7.jpg');
height: 500px;
background-repeat: no-repeat;
background-size: cover;
background-position: center center;
}
http://codepen.io/anon/pen/NbPxzE