[leadingthenet]

The OS probably doesn’t disallow any such thing, but several apps have found workarounds such as briefly setting the screen dark when it detects a screenshot, or various other forms of trickery.

The result is that the screenshot still gets taken (they have no way of disabling that), but the photo is unusable.

[nahqz]

Also, the OS shouldn't tell the foreground app when a screenshot is being taken.

[leadingthenet]

Agreed, but there’d probably be an uproar from the content providers, and neither Apple nor Google has an incentive to be on the users side on this one :/