Good counter example, but what are the chances of getting such a perfect example in the real world? That was constructed with the aim of landing 50% below the mean. Nature has no such purpose.

It's a skewed normal, with the mean at 100 and at least one person over 200, for 50% to be below the mean you'd need one with a negative IQ.

So it is likely that far /more/ than 50% have below average intelligence otherwise you need somebody who actually removes intelligence from the universe.

Or is that what politicians are for?

You might want to blur the image (and blur the inverse). This will allow for minor camera pan or rotation but you'll need a fairly high threshold. The thickness of the hands determines the blur kernel size and just how high is the threshold.

You have known lighting conditions and a strictly limited camera orientation and object configurations.

You can take the inverse of the pixel values as they would be if the hands weren't there (you can mock up the pixel values under the hands by hand since you only need an approximate inverse of the background plate). Then you add that inverse to an image and threshold to get black hands on white background.

Now you can use a hough transform to find all potential hands and you know the locations of the centres of the dials so you can sieve the potential hands down to actual hands. You can then do some simple trigonometry as you know which angles relate to which numbers.

Done.