Edit in JSFiddle

<div class="css-slideshow">
    <figure>
        <img src="https://media-mediatemple.netdna-ssl.com/wp-content/uploads/2012/03/sketch-1.jpg" alt="class-header-css3" width="495" height="370" class="alignnone size-full wp-image-172" />
    </figure>
    <figure>
        <img src="http://themarklee.com/wp-content/uploads/2013/10/class-header-semantics.jpg" alt="class-header-semantics" width="495" height="370" class="alignnone size-full wp-image-179" /><figcaption><strong>Semantics:</strong> Giving meaning to structure, semantics are front and center with HTML5. A richer set of tags, along with RDFa, microdata, and microformats, are enabling a more useful, data driven web for both programs and your users.</figcaption> 
    </figure>
  </div>  
<hr>
<div class="css-slideshow">
    <figure>
        <img src="http://themarklee.com/wp-content/uploads/2013/10/class-header-css3.jpg" alt="class-header-css3" width="495" height="370" class="alignnone size-full wp-image-172" /><figcaption><strong>CSS3:</strong> CSS3 delivers a wide range of stylization and effects, enhancing the web app without sacrificing your semantic structure or performance. Additionally Web Open Font Format (WOFF) provides typographic flexibility and control far beyond anything the web has offered before.</figcaption> 
    </figure>
    <figure>
        <img src="http://themarklee.com/wp-content/uploads/2013/10/class-header-semantics.jpg" alt="class-header-semantics" width="495" height="370" class="alignnone size-full wp-image-179" /><figcaption><strong>Semantics:</strong> Giving meaning to structure, semantics are front and center with HTML5. A richer set of tags, along with RDFa, microdata, and microformats, are enabling a more useful, data driven web for both programs and your users.</figcaption> 
    </figure>
  </div>  
<p class="css-slideshow-attr"><a href="http://www.w3.org/html/logo/" target="_top">Images and captions are from the W3C</a></p>

body{
font-family: "HelveticaNeue-Light", "Helvetica Neue Light", "Helvetica Neue", Helvetica, Arial, "Lucida Grande", sans-serif; 
  font-weight: 300;
}
.css-slideshow{
  position: relative;
  max-width: 495px;
  height: 370px;
  margin: 5em auto .5em auto;
}
.css-slideshow figure{
  margin: 0;
  max-width: 495px;
  height: 370px;
  background: #000;
  position: absolute;
}
.css-slideshow img{
  box-shadow: 0 0 2px #666;
}
.css-slideshow figcaption{
  position: absolute;
  top: 0;
  color: #fff;
  background: rgba(0,0,0, .3);
  font-size: .8em;
  padding: 8px 12px;
  opacity: 0;
  transition: opacity .5s;
}
.css-slideshow:hover figure figcaption{
  transition: opacity .5s;
  opacity: 1;
}
.css-slideshow-attr{
  max-width: 495px;
  text-align: right;
  font-size: .7em;
  font-style: italic;
  margin:0 auto;
}
.css-slideshow-attr a{
  color: #666;
}
.css-slideshow figure{
  opacity:0;
}

figure:nth-child(1) {
   animation: xfade 6s 3s infinite;
}
figure:nth-child(2) {
   animation: xfade 6s 0s infinite;
}

@keyframes xfade{
  30% {
    opacity:1;
  }
  60% {
    opacity:0;
  }
}