This plugin for WordPress automatically add the rel="lightbox[ID-OF-THE-POST]" and recovers the image title.
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 Lightbox 2, Shadowbox.js or an other script, or use a plugin like Shadowbox JS.