Even if it were to become a commonplace way to time-protect images, I can't really see Apple making their screenshotting functionality actually deal with it - they'd be doing it just to circumvent this simple security system, it wouldn't have any other benefits. On Android, though (and jailbroken iOS), I can definitely see people writing mods to break this right away.

I don't think that this technique (even in a more complicated form) could ever be exploit-proof. Even with more randomness or noise, a computer can ultimately compute the same averaging that our eyes are doing, and could always get the source image back.

There's an even easier exploit too: just record the screen with another device.