Shay, without going too deep into details, Revive configuration gives you an option to specify both local and remote paths to your images folder. If you choose to host the images on a CDN, most providers (amazon, rackspace) will give you a way to map the drive locally on your master/admin Revive server, where the images are going to be uploaded through the Revive UI. The slave/ad serving nodes only require the remote path to the images folder.