How would you implement an automatic way of the images loading in a pop-up (lightbox/colorbox) window by a click?
You can. As always, there are several ways.

You can implement a Drupal behavior (jQuery script) that finds all images within the content and adds according classes / click callbacks.

Another way would be writing a little custom module implementing a content filter that does the same on your server.

I'm not at a PC right now. But I think you have two viable ideas now to search for. Let me know, if you need further help.