关键词: 支持向量机, 序贯最小化算法, 选择工作集, 核函数, 多类分类, 验证码识别

Abstract: The usage of verified code is to distinguish between human and machine behavior，which can be used to prevent the malicious behaviors of web robot.The emergence of verified code also makes a number of new types of jobs.The development of e-commerce needs a certain way to promote its goods，and disabilities need urgent attention;thus，many people begin to study web robot technology.They hope that it can realize automatic registrations for email systems，multi-send messages，automatic flood-blogging and auto-login et al.At present，various types of web systems make use of verified code to prevent robots invasion，so the verified code recognition technology is a research hotspot.Based on SVM（Support Vector Machine），a verified code recognition algorithm is proposed，and the experimental results show that the algorithm is efficient.

Key words: Support Vector Machine（SVM）, Sequential Minimization Optimization（SMO）, working set selection, kernel function, multi-class classification, verified code recognition