This made me think of The Thing, a fascinating listening device made by the Soviets that was completely passive until powered remotely. Very difficult to detect when unpowered.

https://en.wikipedia.org/wiki/The_Thing_(listening_device)

And then I thought, something similar might be possible for video. Turns out, yep.

https://ieeexplore.ieee.org/document/8719264

The Eye of Sauron paper does acknowledge the limitations that would likely prevent it from working against such a device. Impressive nonetheless. True privacy/security is just very hard!