<dependency>
  <groupId>com.google.code.kaptcha</groupId>
  <artifactId>kaptcha</artifactId>
  <version>2.3</version>
  <classifier>jdk15</classifier>
</dependency>

<bean id="verifyCodeProducer" class="com.google.code.kaptcha.impl.DefaultKaptcha">
    <property name="config">
      <bean class="com.google.code.kaptcha.util.Config">
        <constructor-arg>
          <props>
            <prop key="kaptcha.border">yes</prop>
            <prop key="kaptcha.border.color">105,179,90</prop>
            <prop key="kaptcha.border.thickness">1</prop>

            <prop key="kaptcha.noise.color">blue</prop>

            <prop key="kaptcha.image.width">150</prop>
            <prop key="kaptcha.image.height">50</prop>

            <prop key="kaptcha.session.key">verifyCode</prop>

            <!-- <prop key="kaptcha.textproducer.char.string">0123456789abcdefghijklmnopqrst!@#$%^*</prop> -->
            <prop key="kaptcha.textproducer.char.length">4</prop>
            <prop key="kaptcha.textproducer.char.space">4</prop>


            <prop key="kaptcha.textproducer.font.size">30</prop>
            <prop key="kaptcha.textproducer.font.color">blue</prop>

          </props>
        </constructor-arg>
      </bean>
    </property>
  </bean>

@Controller
public class CommonController {

  @Autowired
  private Producer verifyCodeProducer;

  @RequestMapping(path = "/getVerifyCodeImage", method = RequestMethod.GET)
  public void getVerifyCodeImage(HttpServletRequest request, HttpServletResponse response) {
    HttpSession session = request.getSession();

    ResponseUtils.noCache(response);
    response.setContentType("image/jpeg");

    String capText = verifyCodeProducer.createText();
    session.setAttribute(Constants.SESSION_KEY_VERIFY_CODE, capText);

    BufferedImage bi = verifyCodeProducer.createImage(capText);
    ServletOutputStream out = null;
    try {
      out = response.getOutputStream();
      ImageIO.write(bi, "jpg", out);
      out.flush();
    } catch (Exception ex) {
      LOGGER.error("Failed to produce the verify code image: ", ex);
      throw new ServerInternalException("Cannot produce the verify code image.");
    } finally {
      IOUtils.closeQuietly(out);
    }
  }
}

<div class="form-group has-feedback">
  <span class="glyphicon glyphicon-barcode form-control-feedback"></span> 
  <input id="verifyCode" name="verifyCode" type="text" maxlength="4" class="form-control" placeholder="<spring:message code='login.label.code' />" />
  <div style="height: 1px"></div>
  <img src="${pageContext.request.contextPath}/getVerifyCodeImage" id="verifyCodeImage" style="margin-bottom: -3px" /> 
  <a href="#" rel="external nofollow" onclick="changeVerifyCode()"><spring:message code='login.code.tip' /></a>
</div>

function changeVerifyCode() {
  $('#verifyCodeImage').hide().attr('src', '${pageContext.request.contextPath}/getVerifyCodeImage?' + Math.floor(Math.random()*100) ).fadeIn(); 
  event.cancelBubble=true; 
}