原生PHP生成验证码

<?php
//生成随机的字符串
    function get_str($len = 4)
    {
        $char = "1234567890abcdefghijklmnoqrstuvwsyzABCDEFGHIJKLMNOPQRSTUVWSYZ";
        $str = str_shuffle($char); //将字符串打乱
        $str = substr($str, 0, $len); //截取四位字符串
        return $str;
    }

//验证码函数
    function img_code($width = 76, $height = 30)//1.定义验证码宽高默认值
    {
        
//2.创建
        $img = imagecreatetruecolor($width, $height);
        
//3.验证码添加背景颜色和文字颜色---imagecolorallcoate()
        $bgcolor = imagecolorallocate($img, 200, 200, 200);
        $textcolor = imagecolorallocate($img, 255, 0, 0);
        
//4.指定图片上画矩形---imagefilledrectangle()
        imagefilledrectangle($img, 0, 0, $width, $height, $bgcolor);
        
//5.将文字放入图片
        $code = get_str();
        imagestring($img, 5, 20, 5, $code, $textcolor);
        
//6.图片上面加一些点
        for ($i = 0; $i < 30; $i++) {
            $dotcolor = imagecolorallocate($img, mt_rand(0, 155), mt_rand(0, 155), mt_rand(0, 155));
            imagesetpixel($img, mt_rand(0, $width), mt_rand(0, $height), $dotcolor);
        }
        
//7.画线
        for ($i = 0; $i < 2; $i++) {
            $linecolor = imagecolorallocate($img, mt_rand(0, 155), mt_rand(0, 155), mt_rand(0, 155));
            imageline($img, mt_rand(0, $width), mt_rand(0, $height), mt_rand(0, $width), mt_rand(0, $height), $linecolor);
        }
        
//将验证码存入session
        session_start();
        $_SESSION['imgcode'] = strtolower($code);
        
//输出图像
        header('Content-Type:image/jpeg');
        imagejpeg($img);
        
//销毁图像，释放内存
        imagedestroy($img);
    }
//调用验证码函数查看验证码
    img_code();