1. A computer-implemented method for analyzing a sequence of video frames depicting a scene captured by a video camera, the method comprising: classifying each of a plurality of pixels in a first frame of the sequence of video frames as depicting one of scene background and scene foreground, wherein each pixel is classified based on a comparison of (i) a relative deviation determined using a pixel value from the first frame and a corresponding pixel value in a background image and (ii) a classification threshold assigned to each pixel in the background image; and upon determining that a group of pixels in the first frame were classified as depicting scene foreground as a result of a sudden illumination change (SIC): for each pixel in the group of pixels: re-classifying the pixel as depicting scene background, and decreasing the classification threshold assigned to the pixel to a value below the relative deviation determined for the pixel; and for one or more successive frames of video following the first frame: updating the pixel values in the background image corresponding to the group of pixels, based on pixel values obtained from video frames following the first frame, and increasing the classification threshold assigned to pixels in the background image for pixels corresponding to the group of pixels.