Using Drawing to create a graphic verification code does not display - asp.net-core

Question

I am developing an API tool for generating verification codes. I use the Drawing package. I have found some methods, but why can't I generate the graphic verification codes I need? Where am I doing wrong?
public void Output(HttpResponse objHttpResponse)
{
using (Bitmap bitmap = this.GetImage())
{
if (bitmap != null)
{
using (MemoryStream ms= new MemoryStream())
{
bitmap .Save(ms, ImageFormat.Jpeg);
HttpContext.Current.Response.ClearContent();
HttpContext.Current.Response.ContentType = "image/Jpeg";
HttpContext.Current.Response.BinaryWrite(ms.ToArray());
HttpContext.Current.Response.Flush();
HttpContext.Current.Response.End();
}
}
}
}

Answer 1

I have a complete code for generating verification code using Bitmap, you can refer to the following:
Controller:
[ApiController]
public class CaptchaController : Controller
{
[Route("get_captcha")]
public Object VerifyCode()
{
string code = "";
Bitmap bitmap = Captcha.CreateCaptcha(out code);
MemoryStream stream = new MemoryStream();
bitmap.Save(stream, ImageFormat.Gif);
return File(stream.ToArray(), "image/gif");
}
}
API to generate verification code:
public class Captcha
{
public static Bitmap CreateCaptcha(out string code)
{
//Create a Bitmap object and draw
Bitmap bitmap = new Bitmap(200, 60);
Graphics graph = Graphics.FromImage(bitmap);
graph.FillRectangle(new SolidBrush(Color.White), 0, 0, 200, 60);
Font font = new Font(FontFamily.GenericSerif, 48, FontStyle.Bold, GraphicsUnit.Pixel);
Random r = new Random();
string letters = "0123456789";
StringBuilder sb = new StringBuilder();
//Add random 4 numbers
for (int x = 0; x < 4; x++)
{
string letter = letters.Substring(r.Next(0, letters.Length - 1), 1);
sb.Append(letter);
graph.DrawString(letter, font, new SolidBrush(Color.Black), x * 38, r.Next(0, 15));
}
code = sb.ToString();
//Confuse the background
Pen linePen = new Pen(new SolidBrush(Color.Black), 2);
for (int x = 0; x < 6; x++)
graph.DrawLine(linePen, new Point(r.Next(0, 199), r.Next(0, 59)), new Point(r.Next(0, 199), r.Next(0, 59)));
return bitmap;
}
}
Result: