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Unfortunately, all of the pixels in that image have noise. Typical image noise is what is called Gaussian noise. The noise follows a Gaussian distribution. So all pixels have noise, but most have amounts close to zero. The wider the spread of values (the wider the gaussian distribution) the more noisy an image appears. Most work focuses on estimating the width of the gaussian distribution, properly called the standard deviation.

HERE is a paper on estimating noise, and there are surely more a google search away.