Abstract: A method of assessing the quality of metal parts, for example through detection of defects in a metal part induced by processing the metal part, comprises acquiring a thermal image of the metal part after processing the metal part, determining a difference image by comparing the thermal image to a reference image, the difference image being related to temperature differences between temperature data represented by the thermal image and by the reference image, and determining a gradient image using the difference image, the gradient image representing temperature difference gradients within the difference image. An example apparatus comprises a camera, such as a thermal camera, an image processor, and an output device such as a display.