.Net Core 实现验证码功能

可以实现以下功能:
Open jpg, bmp, ico, png
Save jpg, bmp, ico, png
Resize image
Draw graphics with brush and pen
Open font and drawstring

//写入 Session、验证码加密
//WebHelper.WriteSession(“session_verifycode”, Md5Helper.MD5(chkCode.ToLower(), 16));
// 创建画布
Bitmap bmp = new Bitmap(codeW, codeH);
Graphics g= Graphics.FromImage(bmp);
g.Clear(Color.White);
// 画噪线
for (int i = 0; i < 1; i++)
{
   int x1 = rnd.Next(codeW);
   int y1 = rnd.Next(codeH);
   int x2 = rnd.Next(codeW);
   int y2 = rnd.Next(codeH);
    Color clr= color[rnd.Next(color.Length)];
    g.DrawLine(new Pen(clr), x1, y1, x2, y2);
}
// 画验证码字符串
for (int i = 0; i < chkCode.Length; i++)
{
   string fnt = font[rnd.Next(font.Length)];
    Font ft= new Font(fnt, fontSize);
    Color clr= color[rnd.Next(color.Length)];
    g.DrawString(chkCode[i].ToString(), ft,new SolidBrush(clr), (float)i * 18, (float)0);
}
// 将验证码图片写入内存流，并将其以 “image/Png” 格式输出
MemoryStream ms = new MemoryStream();
try
{
    bmp.Save(ms, ImageFormat.Png);
   return ms.ToArray();
}
catch (Exception)
{
   return null;
}
finally
{
    g.Dispose();
    bmp.Dispose();
}