DefProc

WordPress plugin to automatically add rel=”lightbox” attribute to link wrapped images, as placed into WordPress posts.
This plugin requires lightbox or slimbox (or any lightbox-compatible image handler) to also be installed on your site, either as part of the theme, or via a plugin. If either lightbox, or add-rel-lightbox is not activated at any time, your site will revert gracefully to the standard “open image as new page”.
The plugin currently only works with images placed into posts using the “add media” dialogues, and will only apply to images that are in your media library. However, it will also not interfere with any images that have already have attributes applied to them.
add-rel-lightbox also works with the [gallery] shortcode, adding the rel=”lightbox” attribute to links created by it. Note that you will have to use the <code>[gallery link="file"]</code> format, or select “Image File” when inserting the gallery for lighbox to work as expected. Galleries that link to the attachment page are unaffected by this plugin.
In addition to applying rel=”lightbox”, this plugin will retrieve the media library caption for any images, and correctly escape any html entities, so that the caption is displayed as expected in the lightbox.

add-rel-lightbox

Add rel="lightbox" to <a> wrapped image links in the content and to [gallery] image links, and include captions for lightbox/slimbox

peppolone

WordPress plugin used to overlay images on the current page into neat Javascript-powered overlay popups. 
This plugin includes the new Slimbox 1.64 javascript written by Christophe Beils and got transformed into a WordPress Plugin by me. 
Slimbox is a 7kb visual clone of the popular Lightbox JS v2.4 by Lokesh Dhakar, written using the ultra compact mootools framework. 
It was designed to be small, efficient, more convenient and 100% compatible with the original Lightbox v2.
<a href="http://www.4mj.it/slimbox-wordpress-plugin/" title="Plugin Homepage" rel="nofollow ugc">Plugin Homepage</a>

Slimbox Plugin

Plugin used to overlay images on the current page into neat Javascript-powered overlay popups.

add-rel-lightbox vs Slimbox Plugin