#cf1 {
  position:relative;
  height:350px;
  width:500px;
  margin:0 auto;
  float:left;
}

#cf1 img {
  position:absolute;
  left:0;
  -webkit-transition: opacity 1s ease-in-out;
  -moz-transition: opacity 1s ease-in-out;
  -o-transition: opacity 1s ease-in-out;
  transition: opacity 1s ease-in-out;
}

  @keyframes cf1FadeInOut {
  0% {
  opacity:1;
}
45% {
opacity:1;
}
55% {
opacity:0;
}
100% {
opacity:0;
}
}

#cf1 img.top {
animation-name: cf1FadeInOut;
animation-timing-function: ease-in-out;
animation-iteration-count: infinite;
animation-duration: 10s;
animation-direction: alternate;
}

#cf2 {
  position:relative;
  height:350px;
  width:500px;
  margin:0 auto;
  float:left;
}

#cf2 img {
  position:absolute;
  left:0;
  -webkit-transition: opacity 1s ease-in-out;
  -moz-transition: opacity 1s ease-in-out;
  -o-transition: opacity 1s ease-in-out;
  transition: opacity 1s ease-in-out;
}

  @keyframes cf2FadeInOut {
  0% {
  opacity:1;
}
45% {
opacity:1;
}
55% {
opacity:0;
}
100% {
opacity:0;
}
}

#cf2 img.top {
animation-name: cf2FadeInOut;
animation-timing-function: ease-in-out;
animation-iteration-count: infinite;
animation-duration: 15s;
animation-direction: alternate;
}