tp5 验证码实现

<p class="pass-form-item">
    <label class="pass-label">验证码</label>
    <input type="text" name="verifyCode" class="pass-text-input " placeholder="请输入验证码" >
    <div> 
        <img src="{:captcha_src()}" alt="captcha" id="captcha_img" onclick="this.src='http://<?php echo $_SERVER['HTTP_HOST']; ?>/tp/public/index.php/captcha?_='+ new Date().getTime();"> 
        <span onclick="captcha_img.src='http://<?php echo $_SERVER['HTTP_HOST']; ?>/tp/public/index.php/captcha?_='+ new Date().getTime();"><a href="###">看不清，换一张</a></span>
    </div>
</p>

$_SERVER['HTTP_HOST'] ----- 获取当前页面域名；