“captcha.php”没有在本地服务器上生成响应

HTML

HTML

<form action="submit.php" method="post"> 
Comment: <textarea name="coment"></textarea> 
Enter Code <img src="captcha.php"><input type="text" name="vercode" /> 
<input type="submit" name="Submit" value="Submit" /> 
</form>
<form action="submit.php" method=