验证码生成工具——Jcaptcha

<dependency>
    <groupId>com.octo.captcha</groupId>
    <artifactId>jcaptcha</artifactId>
    <version>2.0-alpha-1</version>
</dependency>
<dependency>
    <groupId>com.octo.captcha</groupId>
    <artifactId>jcaptcha-integration-simple-servlet</artifactId>
    <version>2.0-alpha-1</version>
    <exclusions>
        <exclusion>
            <artifactId>servlet-api</artifactId>
            <groupId>javax.servlet</groupId>
        </exclusion>
    </exclusions>
</dependency>