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A Captcha—a completely automatic public Turing test to tell computers and humans apart—is a test that humans can pass but computer programs cannot; such tests are becoming key to defending ecommerce systems.Without them, spammers can, for example, write simple automated scripts to create hundreds of free e-mail accounts with a single command. The e-mail(More)
Kohonen's (1988) unsupervised learning algorithm is successfully applied to the codebook generation problem. The algorithm has shown to provide a codebook that rivals the performance of the codebooks obtained using the conventional Linde-Buzo-Gray algorithm, while requiring a minimum amount of processing. The unsupervised learning algorithm provides the(More)
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