Current my images are like this on the blog
<p><a href="http://site.com/pic.jpg" rel="lightbox[1082]"><img src="http://site.com/pic.jpg" alt="" title="post title" width="400" height="266" class="alignnone size-medium wp-image-10084" /></a>
How can I add a div class around this image?

<div>s? More detail in your question would help. Are you using WordPress.com, or self-hosted? Are you a developer (i.e. you can code a plugin in PHP) or are you an end-user? – MikeSchinkel♦ Sep 16 '11 at 3:24