Will the https://foundthru.com/ setup work for a website with 10 million photos? We would use wordpress in combination with woocommerce and your plugins.
It will be something like: https://www.shutterstock.com/
Yes, your biggest issue will be storage space for the images – you will want to present small images to users but then provide large images if they purchase. So probably you would do this by creating downloadable woocommerce products which contain a zip of the images or just the full size image. Users would see the small image then they purchase and get access to download the large image.