Currently, you can upload all existing images to Cloudinary by going to the local media library of WordPress and click on Upload to Cloudinary or select multiple images and then select Upload to Cloudinary from the Bulk Actions menu.
However, posts and pages are not automatically updated to reference images of Cloudinary. Currently you need to edit your posts, and replace the images with their copy that you uploaded to Cloudinary. It is in our road-map to enhance the migration capabilities of the plugin.
All images uploaded to your Cloudinary's account and transformed images generated by Cloudinary are available for download at any time. For our paid plans, you can enable automatic backup of all uploaded images to an Amazon S3 bucket owned by you. Automatically migrating existing posts and pages to stop referencing cloud-based images is currently not supported.