The study compares two types of fatigue characterization based on infrared thermography, namely harmonic analysis and heat source reconstruction. To this end, CF8M A316 steel specimens were subjected to cyclic uniaxial loading at 19 Hz. The experimental protocol involved a force amplitude increasing sequentially every 20,000 cycles, maintaining the load ratio at 0.5. Temperature fields were measured using two infrared cameras simultaneously. A bolometric camera enabled us to measure the mechanical dissipation associated with fatigue damage throughout the tests. This measurement is based on the heat diffusion equation and time-averaged thermal data. A cooled camera was used to perform a spectral analysis of the temperature variations, which were recorded at 211 Hz over short periods. Amplitudes at one and two times the loading frequency were extracted. For comparison purposes, macroscopic quantities over the specimen’s gauge zone were taken into account. Qualitative agreement was obtained between harmonic analysis and heat source reconstruction. In particular, the two methods converged toward a stress amplitude value relatively close to the fatigue limit of the material.