我最终这样做了。感谢您指引我朝着正确的方向TaW

I ended up doing this. Thanks for pointing me in the right direction TaW

public ActionResult Avatar()
        {
            using (var bitmap = new Bitmap(50, 50))
            {
                using (Graphics g = Graphics.FromImage(bitmap))
                {
                    g.Clear(Color.White);
                    using (Brush b = new SolidBrush(ColorTranslator.FromHtml("#eeeeee")))
                    {

                        g.FillEllipse(b, 0, 0, 49, 49);
                    }

                    float emSize = 12;
                    g.DrawString("AM", new Font(FontFamily.GenericSansSerif, emSize, FontStyle.Regular),
                        new SolidBrush(Color.Black), 10, 15);
                }

                using (var memStream = new System.IO.MemoryStream())
                {
                    bitmap.Save(memStream, System.Drawing.Imaging.ImageFormat.Png);
                    var result = this.File(memStream.GetBuffer(), "image/png");
                    return result;
                }
            }
        }