Methods and apparatus, including computer program products, for detecting malfunction in a thermal camera. A first average response value is determined for a first shutter image captured by an image sensor in the thermal camera. A second average response value is determined of a second shutter image captured by the image sensor in the thermal camera. The first average response value and the second average response value are compared. In response to determining that the first average response value and the second average response value differ by more than a predetermined value, an indication of a malfunction of the thermal camera is provided.