A system for detecting faint perturbations of interest in an image is described. The system includes a memory comprising the image, and a processor. The processor is configured to estimate a local mean and variance for each of a plurality of pixels in the image, analyze a local region of the image, an image mean, and an image variance using a filter bank, thereby generating a plurality of response vectors, determine a likelihood of a local perturbation in the image using a probability distribution based on the plurality of response vectors, and make a classification decision of the local perturbation. The probability distribution is calculated, for each of the plurality of response vectors, based on a response of each of the plurality of response vectors to the estimated local mean and variance for each of the plurality of pixels. Methods and machine-readable media are also described.