Lightbox Plus not working

Trying to get Lightbox Plus to work on my theme, but hitting a wall.

I’ve installed the plugin and checked the settings in Appearance, but lightbox is not auto adding the rel attribute to any new image links in posts. Am I missing something?

Example 1 – Added an image form gallary to a new post and this is what I got.

<a href="http://dreamlandhomes.ca/wp-content/uploads/5703-Elizabeth-A-main.png"><img class="aligncenter size-thumbnail wp-image-1556" alt="5703-Elizabeth-A-main" src="http://dreamlandhomes.ca/wp-content/uploads/5703-Elizabeth-A-main-150x150.png" width="150" height="150" /></a>

I tried adding the attribute manually, but it still didn’t work.

<a href="http://dreamlandhomes.ca/wp-content/uploads/5703-Elizabeth-A-main.png" rel="lightbox[test box]"><img class="aligncenter size-thumbnail wp-image-1556" alt="5703-Elizabeth-A-main" src="http://dreamlandhomes.ca/wp-content/uploads/5703-Elizabeth-A-main-150x150.png" width="150" height="150" /></a>