.img-thumbnail{
position: relative;
z-index: 0;
}

.img-thumbnail:hover{
background-color: transparent;
z-index:50;
}

.img-thumbnail span{
position:absolute;
background-color: #ffffff;
padding: 5px;
left: -1000px;
border: 1px solid #000;
visibility: hidden;
color: black;
text-decoration: none;
}

.img-thumbnail span img{
border-width: 0;
padding: 2px;
}

.img-thumbnail:hover span{
visibility:visible;
top: -300px;
left:-250px;
}