Some years ago I used an analog TV card tuned to an empty channel that was giving seemingly white noise and captured frames to generate entropy. I only used the least significant bit of each RGB value of each pixel.

When I supplied the bits to the diehard testsuite, it complained about a number of patterns and failing tests.

The hash function will of course save you, but it's hard to tell the amount of real randomness that's coming from the sensor.

update: Oh, I may have misunderstood. If the whole images changes in random ways and is secret, then of course this is fine.