Plugin to open all past blog post images in lightbox overlay?

I’ve got a client website which needs a plugin that will open all images in blog posts, retroactively, in lightbox overlays. I have tried Lightbox Plus, wp-jquery-lightbox, and WP Lightbox 2. However, they all seem to require some kind of tag to be inserted into the image while posting the post. My client’s site has many, many past blog posts, and it is impossible to go through each to apply the necessary tags to each image in all of them. Is there one that will do it automatically? Right now, each image just opens into its own, poorly formatted page.

A sample blog post on the site:
https://www.torontomulticulturalcalendar.com/2012/12/22/342-first-nations-idle-no-more-demonstration-in-multicultural-toronto/

Click the image, and you’ll see what I mean. Thanks for any assistance!