Basically, to improve there training, any Microsoft employee can look at your photo history at any time. They don't promise that your photos will be encrypted when sent to Microsoft, or that Microsoft will encrypt them when they're stored. And if any of the photos leak, Microsoft won't admit fault, and you can't sue them if any of your private data gets leaked, because you promised not to use the app for private data. At least, that's how I understand it, though I'm not a lawyer.