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Comment by evan_ | Hacker News Reader

They claim to protect against screenshotting- is that possible? I was under the impression that it was not something app developers were able to prevent.

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It's impossible to 100% protect against copies of media being made.

https://en.wikipedia.org/wiki/Analog_hole

No technology prevents a 3rd phone from taking a picture of the screen of a different phone.

What's the second phone doing in that scenario?

I think the implication is that the 1st phone is the sender and the 2nd phone was the receiver, to parallel how you generally label 1st/2nd/3rd-person or -party.

But I definitely had a laugh about someone holding a crazy 5-phone contraption just to copy images.

You could try blinking different parts of the image on and off really fast.

I actually tried that for a contract project about 10 years ago. It didn't work. If you blink slower than 20 times per second it's really annoying to the user. And if you blink faster than 10 times per second it's pretty easy to take a picture with a long exposure and get the whole image. So there is no blink speed that offers even marginal protection without making the image useless.

Video then. You can't defeat the analog hole.

IIRC Snapchat detects when a screenshot has been made by spotting that the touch event for a finger held down is suddenly cancelled. Maybe they're doing this, then deleting the screenshot?

Though, is it even possible to delete camera roll items for 3rd-party apps?

Edit: Ah, they just notify, not prevent, much like Snapchat:

> They cannot save it to their camera roll; and you will be notified if they ever take screenshots.

Edit 2: The old trick Snapchat used doesn't work since iOS 7. Instead, it hooks a newly-added notification that a screenshot was taken.

I know that Signal (formerly Textsecure) won't let you take a screenshot of any text messages.

Except that it can't prevent you from taking a picture of that phone!! It's security through inconvenience!

That's android.

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