[QuercusMax]

There's a way to prevent this - to my great annoyance, health apps (such as the ubiquitous MyHealth variants) and banking apps can prevent you from taking screenshots or copying text. This is presumably to prevent screen-scraping apps from stealing your private data, but it's really annoying when you're trying to screenshot a QR code for some kind of check-in process.

[checkyoursudo]

That's why you need a second phone to photograph the screen of the first phone.

[josephcsible]

If you root your phone, you can use an Xposed module like DisableFlagSecure to get around apps that do that.