understood but just looking for some assistance with what to hook into - would I be accessing the element through the loop? or in the content template block? and if so where? any clues are appreciated.
What I know that plugin like the easy fancybox does is to auto detect the images using some form over javascript and then open those images in the lightbox when clicked on.
So perhaps you can write some custom code to pick up the frontend images to generate the lightbox for them when they are clicked on.
Apart from this i'm not aware of any specific method or hook that can be used. The images links would already be there on the frontend so some manipulation of this would be needed.