<style type="text/css"> 
 
.gallerycontainer{
position: relative;
/*Add a height attribute and set to largest image's height to prevent overlaying*/
}

<!--
*--------------------------------------------------------*
　　上段表示分　CLASS
*--------------------------------------------------------*
-->
 
.thumbnail img{
border: 1px solid gray;
margin: 0 1px 1px 0;
}
 
.thumbnail:hover{
background-color:transparent;
}
 
.thumbnail:hover img{
border: 0px solid glay;
}
 
.thumbnail span{ /*CSS for enlarged image*/
position: absolute;
background-color:white;
padding: 1px;
left: -1000px;
border: 0px dashed gray;
visibility: hidden;
color: black;
text-decoration: none;
}
 
.thumbnail span img{ /*CSS for enlarged image*/
border-width: 0;
padding: 1px;
}
 
.thumbnail:hover span{ /*CSS for enlarged image*/
visibility: visible;
top: 550px;
left: 25px; /*position where enlarged image should offset horizontally */
z-index: 50;
}

<!--
*--------------------------------------------------------*
　　中段表示分　CLASS
*--------------------------------------------------------*
-->

.thumbnail1 img{
border: 1px solid gray;
margin: 0 1px 1px 0;
}
 
.thumbnail1:hover{
background-color:transparent;
}
 
.thumbnail1:hover img{
border: 0px solid glay;
}
 
.thumbnail1 span{ /*CSS for enlarged image*/
position: absolute;
background-color:white;
padding: 1px;
left: -1000px;
border: 0px dashed gray;
visibility: hidden;
color: black;
text-decoration: none;
}
 
.thumbnail1 span img{ /*CSS for enlarged image*/
border-width: 0;
padding: 1px;
}
 
.thumbnail1:hover span{ /*CSS for enlarged image*/
visibility: visible;
top: 820px;
left: 25px; /*position where enlarged image should offset horizontally */
z-index: 50;
}

<!--
*--------------------------------------------------------*
　　下位段表示分　CLASS
*--------------------------------------------------------*
-->

.thumbnail2 img{
border: 1px solid gray;
margin: 0 1px 1px 0;
}
 
.thumbnail2:hover{
background-color:transparent;
}
 
.thumbnail2:hover img{
border: 0px solid glay;
}
 
.thumbnail2 span{ /*CSS for enlarged image*/
position: absolute;
background-color:white;
padding: 1px;
left: -1000px;
border: 0px dashed gray;
visibility: hidden;
color: black;
text-decoration: none;
}
 
.thumbnail2 span img{ /*CSS for enlarged image*/
border-width: 0;
padding: 1px;
}
 
.thumbnail2:hover span{ /*CSS for enlarged image*/
visibility: visible;
top: 1090px;
left: 25px; /*position where enlarged image should offset horizontally */
z-index: 50;
}

*--------------------------------------------------------*
　　最下位段表示分　CLASS
*--------------------------------------------------------*
-->

.thumbnail3 img{
border: 1px solid gray;
margin: 0 1px 1px 0;
}
 
.thumbnail3:hover{
background-color:transparent;
}
 
.thumbnail3:hover img{
border: 0px solid glay;
}
 
.thumbnail3 span{ /*CSS for enlarged image*/
position: absolute;
background-color:white;
padding: 1px;
left: -1000px;
border: 0px dashed gray;
visibility: hidden;
color: black;
text-decoration: none;
}
 
.thumbnail3 span img{ /*CSS for enlarged image*/
border-width: 0;
padding: 1px;
}
 
.thumbnail3:hover span{ /*CSS for enlarged image*/
visibility: visible;
top: 2050px;
left: 25px; /*position where enlarged image should offset horizontally */
z-index: 50;
}
 
</style>