dotnet add package SkiaSharp --version 1.59.3

internal static byte[] GetCaptcha(string captchaText)
  {
   byte[] imageBytes = null;
   int image2d_x = 0;
   int image2d_y = 0;
   SKRect size;
   int compensateDeepCharacters = 0;
   using (SKPaint drawStyle = CreatePaint())
   {
    compensateDeepCharacters = (int)drawStyle.TextSize / 5;
    if (System.StringComparer.Ordinal.Equals(captchaText, captchaText.ToUpperInvariant()))
     compensateDeepCharacters = 0;
    size = SkiaHelpers.MeasureText(captchaText, drawStyle);
    image2d_x = (int)size.Width + 10; 
    image2d_y = (int)size.Height + 10 + compensateDeepCharacters;
   }
   using (SKBitmap image2d = new SKBitmap(image2d_x, image2d_y, SKColorType.Bgra8888, SKAlphaType.Premul))
   {
    using (SKCanvas canvas = new SKCanvas(image2d))
    {
     canvas.DrawColor(SKColors.Black); // Clear 
     using (SKPaint drawStyle = CreatePaint())
     {
      canvas.DrawText(captchaText, 0 + 5, image2d_y - 5 - compensateDeepCharacters, drawStyle);
     }
     using (SKImage img = SKImage.FromBitmap(image2d))
     {
      using (SKData p = img.Encode(SKEncodedImageFormat.Png, 100))
      {
       imageBytes = p.ToArray();
      }
     }
    }

   }
   return imageBytes;
  }

[HttpGet("/api/captcha")]
public IActionResult Captcha()
{
 var bytes = SkiaCaptcha.Captcha.GetCaptcha("hello world");
 return File(bytes, "image/png");
}