The Centre, Gallery, Left, and Right declarations add images to the article page. The images can either be files inside the directory for the target website, or files relative to the file for the article page.
If the image is relative to the article then it will be copied
to the website directory, scaling it if necessary so it is
no larger than the dimensions given by parameters
"IMAGE_MAX_WIDTH" and "IMAGE_MAX_HEIGHT".
The image is
generated inside a link which can be clicked to display the full
image using Lightbox2.
There's a helpful IBM article on using Lightbox2.
I modified lightbox.css (full web URLs for the previous and
next images) screen.css (full web URL for the bg-checker.png
image) and lightbox.js (full URLs for loading.gif
close.png images). With these changes different directories
seem able to use the same lightbox installation.