Abstract: This specification generally relates to methods and algorithms for detection of chemical, biological, and/or radiological attacks. The methods use one or more sensors that can have visual, audio, and/or thermal sensing abilities and can use algorithms to determine by behavior patterns of people whether there has been a chemical, biological and/or radiological attack.

Abstract: A first set of unknown pixels is determined for which being located in the foreground portion does not in-and-of-itself determine the pixel to be part of the foreground. A second set of unknown pixels is determined for which being in a current background portion does not in-and-of-itself determine the pixel to be part of the background. A determination is made for the first and second set of unknown pixels whether the pixel is part of the background or foreground based on temporal data. Extracting an image of the foreground that does not include the current background based on the determination of whether the pixel is part of the foreground, the current background, and temporal data. In an embodiment, the system can use multiple types of sensors to determine whether an entity is a likely security risk.