Is there a way to delete/purge all generated image style images without re-generating them? I'd like to delete all generated image style images without re-generating them immediately.  I want to do this in order to remove them from my backups, because as the number of files on the site increases, it's taking up an exceedingly large amount of space.

I also have the option of making the backup script more complicated and not backing up those directories, but I was wondering if there is a quick way just to remove the generated files only.
You just have to do drush image-flush --all. Source : http://www.drushcommands.com/drush-6x/image/image-flush

Examples of using the drush image-flush command:


drush image-flush - Pick an image style and then delete its images.
drush image-flush thumbnail - 'Delete all thumbnail images.
drush image-flush --all - 'Flush all derived images. They will be regenerated on the fly.'