1. A method of automatically detecting a persistent change in a dynamically varying scene observed by a camera, said method comprising: obtaining a first set of one or more reference images of the scene; transforming the reference images into an abstract feature space such that each pixel thereof is transformed so as to be defined by a set of parameters including at least one parameter which represents at least one of a location of the pixel being transformed, an intensity of the pixel being transformed, a hue of the pixel being transformed, a visual appearance of the pixel being transformed, a texture associated with the pixel being transformed or a local entropy in a visual appearance of pixels in a neighborhood of said pixel being transformed; classifying each pixel of the reference images in the abstract feature space into one of a plurality of classifications, wherein each pixel being classified is classified in response to the parameters defining said pixel being classified; generating a stable reduced-reference image based on the classifications of corresponding pixels across the reference images; obtaining a second set of one or more test images of the scene; transforming the test images into the abstract feature space such that each pixel thereof is transformed so as to be defined by a set of parameters including at least one parameter which represents at least one of a location of the pixel being transformed, an intensity of the pixel being transformed, a hue of the pixel being transformed, a visual appearance of the pixel being transformed, a texture associated with the pixel being transformed or a local entropy in a visual appearance of pixels in a neighborhood of said pixel being transformed; classifying each pixel of the test images in the abstract feature space into one of the plurality of classifications, wherein each pixel being classified is classified in response to the parameters defining said pixel being classified; generating a stable test image based on the classifications of corresponding pixels across the test images; and comparing the stable reduced-reference and test images to one another to detect a difference therein, said difference corresponding to a persistent change in the dynamically varying scene occurring between when the reference images were obtained and when the test images were obtained; wherein the parameters in each set of parameters include: a pair of coordinates which represent the location of the given pixel to which the pair of coordinates relate, an L component of the given pixel to which the L component relates in the Lab color space which represents the intensity of the given pixel to which the L component relates, a and b components of the given pixel to which the a and b components relate in the Lab color space which represent the hue of the given pixel to which the a and b components relate, and a local entropy of the L, a and b components of pixels in a neighborhood of the given pixel to which the local entropy relates which represents the texture associated with the given pixel to which the local entropy relates.