I mean, that's not really how it works. You about fixed it with "If it's anywhere on the internet," though. You can most definitely take photos and keep them locally without anyone ever seeing them. There are ways to hide photos from your albums and password protect them and not have them show up anywhere else or have them uploaded to the internet anywhere. If it's not uploaded to the internet and you didn't send it to anyone, it's safe from leaks. That includes iCloud and Google Photos backup, that's the internet and could theoretically be prone to hacks and whatnot. But you can definitely control it locally and even if your phone is stolen have them safe from unwanted eyes.