Embodiments herein relate to identifying whether a threshold amount of material is on a surface. In particular, an apparatus may have an inspection module to receive an image of a surface captured by a camera, where the surface is illuminated by a light source positioned at an angle to the surface. The apparatus may then analyze the received image to identify a measurement of light intensity of one or more portions of the surface; and determine, based on the analysis, whether each of the one or more portions of the surface includes a threshold amount of a material on the surface.