ThinkPHP验证码插件如何安装

'verify' =>[
    //使用中文验证码
    'useZh'=>false,
    //验证码字体大小(px)
    'fontSize'=>25,
    //验证码位数
    'length'=>5,
    //验证码图片宽度(像素)
    'imageW'=>0,
    //验证码图片高度(像素)
    'imageH'=>0,
    //关闭验证码杂点 
    'useNoise'=>true,
    //背景颜色(16进制色值)
    'bg'=>[243, 251, 254],
    //需要包含的字符集合
    'codeSet'=>'0123456789',
    //验证码字符间隔(px)
    'seKey'=>"ThinkPHP.CN_",//密钥
    ...
],

$img = ( new \Think\Verify())->entry();  
echo $img;

class VerifyCode
{
    //验证码字符长度
    private $length = 4;

    //验证码字符数组
    private $codes = [];

    //验证码生成
    public function generate()
    {   
        //生成字符数组
        $this->codes = [];
        for($i = 0; $i < $this->length; ++$i) {
            $this->codes[] = chr(mt_rand(48, 57));
        }

        //保存字符数组到session中
        session('verifycode', implode('', $this->codes));

        //开启输出缓存
        ob_start();
        header('Content-Type:/image/png');

        //创建验证码图片
        $image = imagecreate(100, 40);

        //设置画布背景颜色 
        $bg_color = imagecolorallocate($image, 238, 238, 238); 
        imagefill($image, 0, 0, $bg_color);

        //绘制验证码字符
        for($i = 0; $i < $this->length; ++$i) {
            $font_file = '/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf';
            $text_color = imagecolorallocate(
                $image, mt_rand(0, 150), mt_rand(0, 150), mt_rand(0, 150));
            imagettftext($image, 24, mt_rand(-20, 20), 5 + $i * 25, 30, 
                         $text_color, $font_file, $this->codes[$i]);
        }

        //输出验证码图片
        imagepng($image);
        imagedestroy($image);
        $img = ob_get_contents();
        ob_end_clean();

        return $img;
    }
}

$vf = new VerifyCode();
echo $vf->generate();