The aim of the paper is the calorimetric detection of fatigue localization zones for an aluminium alloy starting from the thermal images provided by an infrared camera. By means of a local expression of the heat equation and a specific data processing the dissipative and coupling sources accompanying the fatigue test were separately estimated. The processing is based on local approximations of the temperature fields using a set of functions taking account of the spectral properties of the searched sources. The analysis of thermoelastic sources distribution allowed us to point out the heterogeneous character of fatigue phenomena since the beginning of fatigue test. We observed that the zones where thermoelastic sources amplitudes are the most important are the potential loci of the fatigue crack onset.