A method for thermally imaging a moving workpiece of a gas turbine engine using long wavelength infrared (LWIR) images of the workpiece captured during operation of the gas turbine engine. The method comprises determining average pixel intensity and pixel variation in intensity for each pixel across the plurality of LWIR images, determining average area intensity and area variation in intensity across a range of areas defined by increasing length scales about a selected pixel, and identifying as a critical length scale a length scale at which area variation in intensity is minimized as a function of length scale, for which the area intensity remains substantially the same as the average pixel intensity of the selected pixel. A composite image is built such that each pixel of the composite image has intensity equal to an average area intensity centered on that pixel, over the critical length scale.