Methods and systems are provided for locating objects within a content stream, by transforming prospective objects and evaluating the results to identify meaningful semantic values. Transformation is accomplished using various contour transformations, possibly in combination with other tools and techniques. The semantic values produced by contour transformation can be efficiently searched and classified against a dictionary of archetypes to identify objects and object features in the content stream. Contour transformations may be scale-invariant and/or rotationally invariant or otherwise symmetric, so that distinctions between content objects based on their scale or orientation are avoided.