script type="text/javascript"> 
function changeImage(){ 
  var img = document.getElementById("imgVcode");
  if(img.name == 1){ 
    img.name = 2; 
    img.src = "shop.do?method=registerImage2";
  }else if(img.name == 2){ 
    img.name = 1; 
    img.src = "shop.do?method=registerImage";
  } 
} 
/script>

td> 
  img class="yzm_img" id='imgVcode' name="1" src="shop.do?method=registerImage" />
  input name="code" type="text" id="txtVerifyCode" 
    class="yzm_input" onblur="testCode(this)"/>
  div class="text_left t1">
    p class="t1">
      span id="vcodeValidMsg">请输入图片中的四个字母。/span> 
      span id="codeInfo" style="color:red">/span> 
      a href="#" id="imgchange" onclick="changeImage()">看不清楚？换个图片/a>
    /p> 
  /div> 
/td>

public ActionForward registerImage(ActionMapping mapping, ActionForm form, 
   HttpServletRequest request, HttpServletResponse response)
    throws Exception { 
    //将image创建,返回认证码 
    response.setContentType("image/jpeg"); 
    OutputStream out = response.getOutputStream(); 
    String strEnsure = shopManager.createImageInfo(50,20,out);
    //设置到session中 
    request.getSession().setAttribute("strEnsure", strEnsure);
    return null; 
  } 
  public ActionForward registerImage2(ActionMapping mapping, ActionForm form, 
      HttpServletRequest request, HttpServletResponse response)
      throws Exception { 
    //将image创建,返回认证码 
    response.setContentType("image/jpeg"); 
    OutputStream out = response.getOutputStream(); 
    String strEnsure = shopManager.createImageInfo(50,20,out);
    //设置到session中 
    request.getSession().setAttribute("strEnsure", strEnsure);
    return null; 
}