Systems and methods based on thermal imaging for rapid detection of fever conditions in humans that provide for extremely inexpensive, mass producible, field deployable devices accurate in specific, relatively low temperature ranges, and in particular temperatures near nominal human body temperature. The system may include a thermal imager tailored for the application and a corresponding mass producible controlled temperature calibration source configured to provide real time calibration near the human body temperature of interest. The imager and source are deployed in a way such that target people and the calibration source will be within the imager FOV for fever detection. The combination of real time near measurement temperature calibration, with suitable thermography approaches, yield fast, accurate measurements in the fever range using low cost, easy-to-produce components. In combination with a visible imager and pattern/facial recognition techniques, detection of a human target's facial regions of interest suitable for fever detection can be accurately accomplished.