Steganography is a (fascinating) bitch. There are a lot of ways to hide a message in an image which is very resilient to manipulations like resizing, compression or even the loss of information by actually filming a screen versus taking a screen capture.
If you adjust your approach to not rely on a single picture to reliably convey a short message, but part it out over tens or hundreds of frames in a video, it’s basically impossible to make sure that the message was erased without knowing the algorithms used or rendering the video unwatchable.
It’s an awesome field and nothing new.
That’s certainly one of the takes of all time.
Not even touching the problematic ethics here, you expect China and Russia to simply watch the nuclear warheads rain down on their cities and beg for forgiveness afterwards instead of retaliating?