In this paper, the lock-in thermography method is proposed as a non-destructive method for inspection of the hull and detection of osmotic damage. In order to apply the method, it was necessary to construct a simple controler for halogen lamps via relays. The method was evaluated by a comparative examination of the hull with an ultrasonic method. The proposed method is better because it is a full-field method and eliminates the disadvantages of ultrasonic control such as a weak output signal disturbed by the anisotropic structure of the hull. Furthermore, the method of pulsed thermography in the transmission mode of operation has been proposed as a method for non-destructive testing of high pressure tank. The proposed method was applied on a steel diving bottle, severely affected by corrosion damage. Corrosion damage is a special challenge for thermographic tests because it is shallow and irregular in shape. A step forward has also been made in non-destructive testing of composite materials. Multiple samples with different types of damage were made. Damages differ from each other in the nature of the damage, the depth at which they are located and the shape. All produced samples were examined by pulse thermography and the output signal was smoothed by reconstruction of the thermographic signal. In this part, suggestions are given for the selection of the degree of the polynomial which is used to perform the reconstruction of the signal and the evaluation of the images of the polynomial coefficients in order to select the best image in sequence of the polynomial coefficients. An algorithm for automating NDT testing based on the largest thermal gradient of the thermal image witch defines the boundary between the damaged and undamaged area is also proposed. The algorithm was tested for each sample using selected best image. The method of pulsed thermography was applied to metallic materials with excellent thermal conductivity, wherein high-density photographic flashes were used as a heat source. The depth at which flat-bottomed holes are located is proportional to the blind frequency and is written by the proposed equation. The thermal diffusivity of CFRP composite material and the thermal diffusivity of aluminum were calculated. The values of thermal diffusivity of CFRP materials differ greatly in the literature, so in this paper the thermal diffusivity is calculated in two ways, using different sources of thermal excitation. The results do not deviate significantly, so the obtained values are accepted as correct. When measuring the diffusivity of metallic materials, a source of high energy density must be used as an external heat source and then the values of thermal diffusivity correspond to the values found in the literature. At the very end, the non-destructive testing by the active thermography method was modeled by the finite element method. This model will be used for optimization in which the goal is to determine an unknown thermal parameter of the material (e.g. thermal diffusivity).