Check out this quick JS FIDDLE .
Your html
<ul>
<li>
<div class="caption">this is my caption</div>
<img src='http://dribbble.com/system/users/22122/screenshots/244072/empirestate02_d_teaser.png?1314126367'/>
</li>
<li>
<div class="caption">this is my caption</div>
<img src='http://dribbble.com/system/users/22122/screenshots/244072/empirestate02_d_teaser.png?1314126367'/>
</li>
<li>
<div class="caption">this is my caption</div>
<img src='http://dribbble.com/system/users/22122/screenshots/244072/empirestate02_d_teaser.png?1314126367'/>
</li>
<li>
<div class="caption"><span>this is my caption</span></div>
<img src='http://dribbble.com/system/users/22122/screenshots/244072/empirestate02_d_teaser.png?1314126367'/>
</li>
</ul>
Css
ul li{ float:left; padding:20px; border:solid gray 4px; margin:5px;}
ul li div{display:none; background:white; opacity:.5; position:absolute;}
and your javascript
$('ul li').mouseenter(function(){
var image= $(this).find('img'),
caption = $(this).find('div');
caption.width(image.width());
caption.height(image.height());
caption.fadeIn();
}).mouseleave(function(){
var image= $(this).find('img'),
caption = $(this).find('div');
caption.width(image.width());
caption.height(image.height());
caption.fadeOut();
});
, , . , . , .