What is the difference between ShortPixel Image Optimizer and Autoptimize with its image optimization & CDN by ShortPixel
The ShortPixel Image Optimizer plugin is an image optimization plugin that replaces the local files with their optimized versions. Once the images are optimized, they remain optimized even if you choose to deactivate the plugin.
On the other hand, the Autoptimize plugin with the "Image Optimization" function active will not touch the local files. Instead it will optimize on-the-fly and serve the images from the ShortPixel CDN. Deactivating the "Image Optimization" option on Autoptimize or deactivating the Autoptimize plugin altogether, means that the website will start serving the old, un-optimized images immediately.