Abstract: Methods and apparatus, including computer program products, for threat detection based on radiation contrast. In general, an image from a device having a sensitivity to infrared radiation having a wavelength between three and fifteen micrometers may be received, images features from the image may be extracted, a classification may be generated of the image features from multiple classifications where the classifications include threats, and data characterizing the classification of the image features may be displayed. The device may operate at a standoff distance of five to one hundred meters. Displaying data characterizing the classification of the image features may include displaying an identification of a person carrying a threat.