Mdkart

This plugin for WordPress automatically add the rel=”lightbox[ID-OF-THE-POST]” to images linked in a post 
ID-OF-THE-POST is unique per post so all images per post are grouped in one lightbox set. 
Works also with the gallery Fonction of WP 2.7 and in comments
Doesn’t add the the files required for Lightbox (it only add the rel lightbox tag)! You have to insert yourself in your theme the required files or use a plugin like Lightbox 2 WordPress Plugin or Lightbox 2.3 plugin for WordPress
<h3>Changelog / Todo</h3>
0.4.1 
* Optimizing the code 
0.4 
* Now Compatible with the Gallery Fonction of WP 2.7 
* Adds also rel tag in the comments 
0.3 
* Correction of a bug that added rel tag on links done on img tags. 
0.2 
* Correction of a small bug described by Kristof Mattei. Thanks to him for the help!
Thanks to all who sent bug reports and ideas for improvements. 
Please send me a mail if I forgot you to mention here.

Add Lightbox

This plugin for Wordpress automatically add the rel="lightbox[ID-OF-THE-POST]" to images linked in a post

ppalli

This plugin automatically add the rel=”lightbox[POST-ID]” to images linked in a post and in a comment, and recovers the image title. 
POST-ID is unique per post so all images per post are grouped in one LightBox set. 
Doesn’t add the files required for LightBox, it’s add the “rel lightbox” tag. 
You have to insert the required files yourself in your theme, you can use <a href="http://www.huddletogether.com/projects/lightbox2/" rel="nofollow ugc">Lightbox 2</a>, <a href="http://www.shadowbox-js.com/" rel="nofollow ugc">Shadowbox.js</a> or an other script, or use a plugin like <a href="https://wordpress.org/extend/plugins/shadowbox-js/" rel="ugc">Shadowbox JS</a>.

Add LightBox & Title

This plugin for WordPress automatically add the rel="lightbox[ID-OF-THE-POST]" and recovers the image title.

Add Lightbox vs Add LightBox & Title