Cache busting for images in Drupal 7 and lightbox 2
OK, I solved it. Cachebuster can be implemented as discussed in shared url for drupal 7 by editing includes/theme.inc, and theme_image function. Just add attributes['src']with a random string say time().
Further, lightbox2 module can be tweaked to append random string in a href, by editing lightbox2/js/lightbox.js, just edit start: function(imageLink, slideshow, lightframe, lightvideo, lightmodal) {} and append anchor.href with new Date().getTime().

These two tweaks will make sure that drupal is giving img src appended with time and lightbox2 inserting time() in anchor href.
Browser will never cache these images.