/*#contenido img{width:300px;margin-top:10px;margin-bottom:200px;margin-left:50px;margin-right:10px;float:left;}*/
#contenido{font-size:12px;}

<style type='text/css'> 
.thumbnail{ position: relative; z-index: 0; }
.thumbnail:hover{ background-color: transparent; z-index: 10; }
 .thumbnail span{ /* Estilos para la imagen agrandada */ position: absolute; background-color: black; padding: 5px; left: -100px; border: 5px double gray; visibility: hidden; color: #ffffff; text-decoration: none; } 
 .thumbnail span img{ border-width: 0; padding: 2px; } 
 .thumbnail:hover span{ visibility: visible; top: -100; left: 20px; } 
 </style>table{margin-top:200px;}
h3{margin-top:30px;
}