关于那些表单的验证码

    验证码是一些注册、登录等表单常用的一个功能，为了防止一些恶意性的填写表单，不断地提交表单，造成安全隐患。验证码一般随机可以切换验证码图片，经过远程验证成功后才能成功提交表单。实现了简单的验证码功能

<form>

<div class="joinCon"><div class="row"><div class="label"><em class="musTip">*</em>用户名：</div><div class="cell"><input type="text" data-checkurl="/supajaxcheck/checkusername" name="username" class="inTxt"></div></div><div class="row"><div class="label"><em class="musTip">*</em>密码：</div><div class="cell"><input type="password" name="password" class="inTxt"></div></div><div class="row"><div class="label"><em class="musTip">*</em>确认密码：</div><div class="cell"><input type="password" name="repassword" class="inTxt"/></div></div><div class="row verBox "><div class="label"><em class="musTip">*</em> 验证码：</div><div class="cell verCode"><input type="text" data-checkurl="/joinin/checkcode" class="inTxt w115 fl n-invalid" name="key" ><div class="checkCode"><img src="/joinin/captcha/v/5449ad3ebee49" id="KeyImg" class="checkPic" style="cursor:pointer" title="点击换图" alt="点击换图">                                <a href="javascript:return false;">换一张</a></div></div></div></div>

html表单怎么弄验证码、

</form>

js代码片段：

var verCode = $('div.verCode','form');verCode.each(function(){var box = $(this),img = $('img.checkPic', box),src = img.attr('src'),chg = $('a', box),ipt = $('input.checkCode', box);chg.on('click', function(e) {e.preventDefault();e.stopPropagation();var _src = src+'&'+$.now();img.attr('src', _src);});img.on('click', function(e) {e.preventDefault();e.stopPropagation();var _src = src+'&'+$.now();img.attr('src', _src);});});

表单验证码是什么意思？