From the description of the plugin:
“This is a Lightbox2 plugin and it adds
rel=“lightbox”to single- or doublequoted imagelinks automagically. Credits: MacRabbit‘s Lightbox mod, turned into plugin by Várkonyi Balázs. Optimized image pre-processor by Bramus, because Manuel Martensen is a notorious pain in the ass (but a handsome one) and made him do it.”
Fancy! Need to fool around with this for a while once I start digging back into web development.