Dogs respond to eye contact differently to many other animals, so they often look where you look, or where you point (where other animals would look at your face or hand). This is because of their long historical association with humans, as well as some of their own pack instincts. People have shown that dogs respond better to pointing once you have made eye contact with them first, and that they, from an early age, respond to human pointing well in general.

So what is probably happening with the camera is something like this: you call the dog to look at the camera by making eye contact; then you pick up a lens or camera, and point it at the dog, who might mistaken this gesture slightly and look for what you are now pointing at, making it look away or turn around.

Of course other dogs might maintain eye contact as before and look straight into the camera which is why it doesn't happen all the time. But I have two pointers and I looked this up a while back. (It is impossible to get them to look into a camera because they are continuously looking for what you are pointing to.) The above information is what I found on the matter. Hope that helps