Various techniques are provided to process captured thermal images to determine whether the thermal images exhibit degradation associated with environmental effects and/or security conditions. In one example, a method includes capturing a plurality of thermal images of a scene. The thermal images are processed to generate first and second background images associated with first and second time periods to filter out changes in the scene occurring within the associated time periods. The first and second background images are edge filtered to generate first and second edge images. The first and second edge images are compared to determine a change in edges associated with the scene. A device is selectively operated in a fail-safe mode in response to the comparing. Additional methods and related systems are also provided.