Edit in JSFiddle

<header>
<img src="http://demosthenes.info/assets/images/thumbnails/valhalla.jpg" alt>
<img src="http://demosthenes.info/assets/images/thumbnails/beached-viking-ship.jpg" alt>
<img src="http://demosthenes.info/assets/images/thumbnails/water-maiden.jpg" alt>
</header>

header{
    border: 4px solid #000;
    font-size: 0;
}