Yes, I was referring to this article.
But I wanted to add more fields in the Image Map Tool Dialog. So earlier I wasn't able to find .js files of the SmartImage widget.
But now I have found those, they reside in the path "/libs/cq/ui/widgets/source/widgets/form/SmartImage" . We can overlay these js files to tweak the SmartImage widget.
Thanks a lot for the help though !