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");
}