[juandazapata]

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

[kazazes]

What's the second phone doing in that scenario?

[XaspR8d]

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.

[astrange]

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

[joshyeager]

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.

[alexbecker]

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