Cameras are actually a fantastic source of entropy because the CMOS sensors produce high quality and very random data in the form of noise. You can crank up the sensitivity (ISO) and get even more.
Increasing the ISO is just a multiplication of the raw sensor value - it doesn't lead to more noise - it just makes it visible to the human eye. Also on my DSLR I can see all kinds of stripes and cross patterns in the noise, so a lot of it is not really random but based on static sensor properties.
Fair enough, it is indeed just an amplifier, but what I was trying to say is that the noise becomes quite visually apparent when you increase the ISO.
you can cancel out static noise with multiple readings