> One method would be to have a unique key burned into the image sensor by the manufacturer. That key will be in turn used to cryptographically sign the raw signal output from the sensor to verify that the image was indeed generated by that specific sensor.

This would be horrible for privacy, although somewhat mitigated if the camera program/app discarded the signature by default.

Yeah it would, and ideally it should be possible for the user to choose to include the signature or not in their images. Though I wouldn't be surprised to see this type of tech being the norm in the future, perhaps in a sneaky way like what they did with printers and digital watermarking (https://en.wikipedia.org/wiki/Machine_Identification_Code). We may even see this in other integrated sensors like a MEMS mic with a built-in AD on the silicon.

This isn't doable. Nothing prevents you from gluing or projecting a screen directly into the sensor, after tone mapping the image properly. There is no winning. It wouldn't even be expensive!

Yes, that has been repeatedly pointed out. And yet the industry still did it and your digital cables carrying video aren't going to work properly without the HDCP DRM.

Yeah, but I can get an HDCP-compliant HDMI capture card for 8$ on Aliexpress, so I really don't care and it really doesn't work. You can also buy splitters that happen to disable HDCP.