Removing the data from several 100,000s of existing images would be a HUGE job, requiring a lot of thought when coding to adapt the code even to the smallest servers. It is not an easy task to extend our add-on with this feature. We are currently not sure if that is even possible to handle with this add-on.
Currently we are thinking of providing a shell script to handle existing images. But nothing near to be released at the moment. Sorry.