Joffrey Quillet

Always Valid Lightbox is a Lightbox plugin which can automatically add the HTML attributes needed to trigger the effect on content image links, so that 
the user never has to add a class or an attribute to his content images in order to make the lightbox work.
Also, AVL allows the user to chose the attributes he wants inserted on his image links, depending on the Doctype declaration used in the website header.php template. 
This way, the lightbox never generates markup validation errors at the W3C Validator test.
The jQuery lightbox effect is an adaptation based on David Ryan’s jQuery lightbox tutorial : http://dryan.com/articles/jquery-lightbox-tutorial/

Always Valid Lightbox

Always Valid Lightbox is a Lightbox plugin whose markup adapts to the WP site's Doctype, in order to always provide valid HTML markup.

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.

Always Valid Lightbox vs Add LightBox & Title