不想说废话，直接源码拿去用。。。  

/// <summary>
    /// 二维码管理
    /// </summary>
    public class QRCoderHelper
    {
        /// <summary>
        /// 生成二维码图片
        /// </summary>
        /// <param name="Content">内容文本</param>
        /// <param name="QRCodeEncodeMode">二维码编码方式</param>
        /// <param name="QRCodeErrorCorrect">纠错码等级</param>
        /// <param name="QRCodeVersion">二维码版本号 0-40</param>
        /// <param name="QRCodeScale">每个小方格的预设宽度（像素），正整数</param>
        /// <param name="size">图片尺寸（像素），0表示不设置</param>
        /// <param name="border">图片白边（像素），当size大于0时有效</param>
        /// <param name="codeEyeColor"></param>
        /// <returns></returns>
        public Image CreateQRCode(string Content, QRCodeEncoder.ENCODE_MODE QRCodeEncodeMode, QRCodeEncoder.ERROR_CORRECTION QRCodeErrorCorrect, int QRCodeVersion, int QRCodeScale, int size, int border, Color codeEyeColor)
        {
            QRCodeEncoder qrCodeEncoder = new QRCodeEncoder();
            qrCodeEncoder.QRCodeEncodeMode = QRCodeEncodeMode;
            qrCodeEncoder.QRCodeErrorCorrect = QRCodeErrorCorrect;
            qrCodeEncoder.QRCodeScale = QRCodeScale;
            qrCodeEncoder.QRCodeVersion = QRCodeVersion;
            Image image = qrCodeEncoder.Encode(Content);

            #region 根据设定的目标图片尺寸调整二维码QRCodeScale设置，并添加边框
            if (size > 0)
            {
                //当设定目标图片尺寸大于生成的尺寸时，逐步增大方格尺寸
                #region 当设定目标图片尺寸大于生成的尺寸时，逐步增大方格尺寸
                while (image.Width < size)
                {
                    qrCodeEncoder.QRCodeScale++;
                    Image imageNew = qrCodeEncoder.Encode(Content);
                    if (imageNew.Width < size)
                    {
                        image = new Bitmap(imageNew);
                        imageNew.Dispose();
                        imageNew = null;
                    }
                    else
                    {
                        qrCodeEncoder.QRCodeScale--; //新尺寸未采用，恢复最终使用的尺寸
                        imageNew.Dispose();
                        imageNew = null;
                        break;
                    }
                }
                #endregion

                //当设定目标图片尺寸小于生成的尺寸时，逐步减小方格尺寸
                #region 当设定目标图片尺寸小于生成的尺寸时，逐步减小方格尺寸
                while (image.Width > size && qrCodeEncoder.QRCodeScale > 1)
                {
                    qrCodeEncoder.QRCodeScale--;
                    Image imageNew = qrCodeEncoder.Encode(Content);
                    image = new Bitmap(imageNew);
                    imageNew.Dispose();
                    imageNew = null;
                    if (image.Width < size)
                    {
                        break;
                    }
                }
                #endregion

                //根据参数设置二维码图片白边的最小宽度（按需缩小）
                #region 根据参数设置二维码图片白边的最小宽度
                if (image.Width <= size && border > 0)
                {
                    while (image.Width <= size && size - image.Width < border * 2 && qrCodeEncoder.QRCodeScale > 1)
                    {
                        qrCodeEncoder.QRCodeScale--;
                        Image imageNew = qrCodeEncoder.Encode(Content);
                        image = new Bitmap(imageNew);
                        imageNew.Dispose();
                        imageNew = null;
                    }
                }
                #endregion

                //已经确认二维码图像，为图像染色修饰
                if (true)
                {
                    //定位点方块边长
                    int beSize = qrCodeEncoder.QRCodeScale * 3;

                    int bep1_l = qrCodeEncoder.QRCodeScale * 2;
                    int bep1_t = qrCodeEncoder.QRCodeScale * 2;

                    int bep2_l = image.Width - qrCodeEncoder.QRCodeScale * 5 - 1;
                    int bep2_t = qrCodeEncoder.QRCodeScale * 2;

                    int bep3_l = qrCodeEncoder.QRCodeScale * 2;
                    int bep3_t = image.Height - qrCodeEncoder.QRCodeScale * 5 - 1;

                    int bep4_l = image.Width - qrCodeEncoder.QRCodeScale * 7 - 1;
                    int bep4_t = image.Height - qrCodeEncoder.QRCodeScale * 7 - 1;

                    Graphics graphic0 = Graphics.FromImage(image);

                    // Create solid brush.
                    SolidBrush blueBrush = new SolidBrush(codeEyeColor);

                    graphic0.FillRectangle(blueBrush, bep1_l, bep1_t, beSize, beSize);
                    graphic0.FillRectangle(blueBrush, bep2_l, bep2_t, beSize, beSize);
                    graphic0.FillRectangle(blueBrush, bep3_l, bep3_t, beSize, beSize);
                    graphic0.FillRectangle(blueBrush, bep4_l, bep4_t, qrCodeEncoder.QRCodeScale, qrCodeEncoder.QRCodeScale);
                }

                //当目标图片尺寸大于二维码尺寸时，将二维码绘制在目标尺寸白色画布的中心位置
                #region 如果目标尺寸大于生成的图片尺寸，将二维码绘制在目标尺寸白色画布的中心位置
                if (image.Width < size)
                {
                    //新建空白绘图
                    Bitmap panel = new Bitmap(size, size);
                    Graphics graphic0 = Graphics.FromImage(panel);
                    int p_left = 0;
                    int p_top = 0;
                    if (image.Width <= size) //如果原图比目标形状宽
                    {
                        p_left = (size - image.Width) / 2;
                    }
                    if (image.Height <= size)
                    {
                        p_top = (size - image.Height) / 2;
                    }

                    //将生成的二维码图像粘贴至绘图的中心位置
                    graphic0.DrawImage(image, p_left, p_top, image.Width, image.Height);
                    image = new Bitmap(panel);
                    panel.Dispose();
                    panel = null;
                    graphic0.Dispose();
                    graphic0 = null;
                }
                #endregion
            }
            #endregion
            return image;
        }
    }

C#&.Net干货分享-构造QRCoderHelper生成二维码图片