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Actually this is a very typical detection task and often answered in this forum. The most answers given: Either train a cascade classifier, see http://docs.opencv.org/doc/user_guide/ug_traincascade.html and the various questions about it on this Q&A forum. Or alternatively, you can try a bag of words approach combined with a classifier, see e.g. http://answers.opencv.org/question/8677/image-comparison-with-a-database#8686.