Thermal imaging is nowadays widely used in many industrial areas for non destructive analysis. This paper focuses on the detection by active thermography of cracks in a transparent and specular piece of glass. A continuous laser scans the target by creating a hot spot that is acquired by a thermal camera. A thermal map is computed by averaging of thermal measurements for all the positions of the hot spot on the target. Then edge filters are applied to highlight the cracks. Experimental results demonstrate the validity of the material damage estimation in a short processing time.