My site hosts/sells hundreds of photos. To optimize the loading of each image in the front-end I decided to use CDN. The plugin I'm using for that is W3 Total Cache. My question is; is it supposed to delete the images after they are uploaded? I was hoping CDN would act like an image hosting too so that my hosting wouldn't have to store the images. Does CDN allow that or it requires retaining a copy of each image in the local server?
The CDN doesn't allow or disallow anything - it doesn't care what you keep on your server. W3 Total Cache does not remove local images after copying them to the CDN - and nor should it. What would happen if your CDN disappeared, or corrupted, or increased it's prices? You'd lose all of your image files.