The planar image of an object can be represented as a "codon" list of maxima, minima and zeros of the image's curvature. This representation is invariant over rotation, translation, scale, and other distortions of the image, making it a useful representation for visual recognition or inspection. Calculating this representation from a digital image is difficult because of the granularity of the image and the possibility of many scales for the object (e.g., a fractal). We present an algorithm for examining a digital image at various scales, computing curvature, and symbolically encoding this information. This algorithm is designed for a digital frame buffer and video arithmetic logic unit.