I'm no expert in cryptography, but my thought is that it isn't enough just to be random. For cryptography, you need a source of randomness (unpredictable) that

I'm no expert in cryptography, but my thought is that it isn't enough just to be random. For cryptography, you need a source of randomness (unpredictable) that cannot be easily manipulated (which could make it predictable to the manipulator). In your example, if I could locate your camera I could put a video I control in front. Now I can direct the outputs to be more predictable to me.