需要引用QRCoder

  [AcceptVerbs("get")]
        [Route("api/UserChannel/GetQR")]
        public HttpResponseMessage QR(string code)
        {
            code = HttpUtility.UrlDecode(code);
            QRCodeGenerator qrGenerator = new QRCodeGenerator();
            QRCodeData qrCodeData = qrGenerator.CreateQrCode(code, QRCodeGenerator.ECCLevel.Q);
            QRCode qrCode = new QRCode(qrCodeData);
            Bitmap qrCodeImage = qrCode.GetGraphic(10, Color.Black, Color.White, null, 15, 6, false);
            MemoryStream ms = new MemoryStream();
            qrCodeImage.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
            qrCodeImage.Dispose();

            HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK);
            result.Content = new ByteArrayContent(ms.ToArray());
            result.Content.Headers.ContentType = new MediaTypeHeaderValue("image/jpg");
            return result;
        }