Optimize JPEGs:

Optimize JPEG images is an optional process that reduced the file size of generated images by up to 20%. It uses MozJPEG 2 or 3(3 recommended).

You can access the function by navigating to your CMS admin panel, Utilities >> Optimize JPEGs.

Your home directory will be filled out but you can change it to focus only a specific parent folder.
You can enter an email address to send a digest report of all files that are modified.
Then click "Process"

The system will attempt to optimize files inside the selected folder, including any files multiple levels deep and inside subfolders of the selected folder.  Source files are also compressed. There is no opt-out for source files.