Simple Gallery only with CSS

<div id="cf">
  <img class="bottom" src="/images/Cirques.jpg" />
  <img class="top" src="/images/Clown%20Fish.jpg" />
</div>

<style>

  @keyframes cf3FadeInOut {
  0% {
  opacity:1;
}
45% {
opacity:1;
}
55% {
opacity:0;
}
100% {
opacity:0;
}
}

#cf3 img.top {
animation-name: cf3FadeInOut;
animation-timing-function: ease-in-out;
animation-iteration-count: infinite;
animation-duration: 10s;
animation-direction: alternate;
}

</style>