Don't trust, verify, but I had Claude compare Pi Zero camera captures with the camera face down on a desk in a dark room. Consecutive captures were mostly black, of course, but still had 74,000 bits of variation between them.
So "a bit of sensor noise" is actually a shit ton. Sensors, especially cheap ones like the Raspi camera, are noisy af.
Second, any photo is going to have variations from shot-to-shot. It's just not possible to take the same pixel-for-pixel photo twice (certainly not from a small handheld device), even if the sensor was somehow immune to noise.
Most people wouldn't opt to use a photo of a blank wall as their image entropy, but the math + sensor reality (plus all the additional preview frames being hashed in) says it's effectively not any worse than, say, a chaotic pic of running water or a pile of sand.
