descriptor and fast character recognition
Shape Context descriptor and fast characters recognition
Matching shapes can be much difficult task then just matching images, for example recognition of hand-written text, or fingerprints. Because most of shapes that we trying to match is heavy augmented. I can bet that you will never write to identical letters for all your life. And look at this from the point of people detection algorithm based on handwriting matching -- it would be just hell. Of course in the age of Neural networks and RNNs it also can be solved in a different way then just straight mathematics, but not always you can use heavy and memory hungry things like NNs.