<p>Vibrothermography using vibration excitation at specific frequency to activate a resonance in a defective area (local defect resonance, LDR) is promising for magnifying vibration induced heating and facilitating the detection of defects. However, the technique is limited by the requirement for a knowledge of vibrational responses to determine the resonance frequency. In this paper, a method for the automated determination of an optimal probing frequency only from surface temperature is proposed. A 3D finite element model and an experimental setup are established. The rate of temperature rise is proposed to better indicate the occurrence of LDR of an artificial delamination in carbon fiber reinforced polymer (CFRP). The defect-to-background contrast (DBC) is defined to quantify the enhancement of thermal imaging. Results from long-pulse vibrothermographic experiments show that the highest signal-to-noise ratio of delamination detection is achieved when the probing frequency is selected at the peak of DBC calculated from the rate of temperature rise. The identified probing frequency is stable for various bandwidths of sweep. The proposed method can improve the signal-to-noise ratio of thermal imaging of delamination in CFRP.</p>