think\File::checkImg PHP Method

    public function checkImg()
    {
        $extension = strtolower(pathinfo($this->getInfo('name'), PATHINFO_EXTENSION));
        /* 对图像文件进行严格检测 */
        if (in_array($extension, ['gif', 'jpg', 'jpeg', 'bmp', 'png', 'swf']) && !in_array($this->getImageType($this->filename), [1, 2, 3, 4, 6])) {
            return false;
        }
        return true;
    }