WP Speed of Light: Image Compression
ImageRecycle is a 3rd party image compression service: https://www.imagerecycle.com/
We've added the service in the WP Speed of Light Speed optimization > Image Compression because we consider it's a big performance improvement but it's not mandatory to use it. Our members can get a 20% OFF coupon on all membership from the configuration page.
After installing, you can compress the image and pdf files at left menu Media > ImageRecycle.
For more information you can go here: https://www.imagerecycle.com/cms/wordpress