Self-calibrating an automatic, surveillance-based change detection system operating on noisy imagery comprises detecting a first image co-registered with a second image, wherein the first image and the second image each comprise pixels of a noisy image of a scene; detecting the second image co-registered with the first image, wherein co-registration of the first image with the second image comprises pixels from different images corresponding to a same location within the scene; producing a calibration factor based on the co-registered images; producing a modified ratio of pixel values corresponding to the first image and the second image from the same location within the scene; and comparing the modified ratio to a pre-determined threshold ratio value.