GD library generates image verification code-PHP Tutorial-php.cn

GD library generates image verification code

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Release： 2023-04-07 17:34:01

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We are no strangers to verification codes. They can be seen everywhere, such as: login and registration, forum flooding, ticket brushing, password cracking, etc. Their main function is to block machine requests and protect business from being interfered by machine submission requests.

Let’s write a verification code demo, using the most common alphanumeric verification code, plus interference points and interference lines. It is generated by using the GD library. If you have not installed it, please install it on Google yourself. , and how to determine whether it is installed and enabled, please search the GD library directly on the phpinfo page

The effect is as shown below:

GD library generates image verification code

##Front page

<?php
if(isset($_REQUEST["code"])){
    session_start();
    if(strtolower($_POST["code"])==$_SESSION["code"]){
        echo "<script>alert(&#39;正确！&#39;)</script>";
    }else{
        echo "<script>alert(&#39;错误！&#39;)</script>";
    }
}
?>
<!doctype html>
<html>
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>验证码</title>
    <style>
        #code{
            border: 1px solid #ccc;
            vertical-align: bottom;
        }
        #refresh{
            text-decoration: none;
            font-size: .875em;
        }
    </style>
</head>
<body>
<form action="" method="post">
    <p>
        验证码：
        <img  src="code.php?r=<?php echo rand()? alt="GD library generates image verification code" >" alt="" id="code">
        <a href="javascript:;" id="refresh">看不清？</a>
    </p>
    <p>
        输入验证码：
        <input type="text" name="code">
    </p>
    <input type="submit" value="提交">
    <script>
        document.getElementById("code").onclick = document.getElementById("refresh").onclick = refresh;
        function refresh() {
            document.getElementById(&#39;code&#39;).src=&#39;code.php?r=&#39;+Math.random()
        }
    </script>
</form>
</body>
</html>

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Backend page

<?php
//启动session
session_start();
$code = "";         //验证码字符串
$str = "qwertyuiopasdfghjklzxcvbnm1234567890";  //验证码字符取值范围[a-z0-9]
$w = 160;           //图片宽度
$h = 40;            //图片高度
$num = 4;           //验证码字符数
$dotNum = 300;      //干扰点个数
$lineNum = rand(3, 5);         //干扰线条数
$font = "./api/DejaVuSansMono.ttf";     //设置字体文件
$image = imagecreatetruecolor($w, $h);  //创建一张指定宽高的图片
$imageColor = imagecolorallocate($image, 255, 255, 255);   //设置背景图片颜色为白色
imagefill($image, 0, 0, $imageColor);  //填充图片背景
//随机验证码，包含字母和数字
for ($i = 0; $i < $num; $i++) {
    $fontColor = imagecolorallocate($image, rand(0, 120), rand(0, 120), rand(0, 120));  //生成随机字体颜色
    $content = substr($str, rand(0, strlen($str)), 1);      //随机取字符集中的值
    $code .= $content;
    $fontSize = rand(15, 25);                    //字体大小
    $x = $i * $w / $num + rand(5, 10);          //指定生成位置X轴偏移量
    $y = rand(20, 30);                          //指定生成位置Y轴偏移量
    imagettftext($image, $fontSize, 0, $x, $y, $fontColor, $font, $content);
}
$_SESSION["code"] = $code;  //保存验证码字符串到session中
//生成干扰点
for ($i = 0; $i < $dotNum; $i++) {
    $dotColor = imagecolorallocate($image, rand(0, 255), rand(0, 255), rand(0, 255));
    imagesetpixel($image, rand(0, $w), rand(0, $h), $dotColor);
}
//生成干扰线
for ($i = 0; $i < $lineNum; $i++) {
    $lineColor = imagecolorallocate($image, rand(0, 100), rand(0, 100), rand(0, 100));
    imageline($image, rand(0, $w), rand(0, $h), rand(0, $w), rand(0, $h), $lineColor);
}
header("content-type:image/png");
imagepng($image);
imagedestroy($image);

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