1.NuGet引入包 ZKWeb.System.Drawing，不会的自己Google。

2、添加cs

cs代码如下：   

using System;
using System.DrawingCore;
using System.DrawingCore.Drawing2D;
using System.DrawingCore.Imaging;
using System.IO;
namespace XXXX.Common.Core.Helper
{   
    public sealed class VerifyCodeHelper
    {        
        #region 单例模式  
        //创建私有化静态obj锁    
        private static readonly object _ObjLock = new object();        //创建私有静态字段，接收类的实例化对象    
        private static VerifyCodeHelper _VerifyCodeHelper = null;        //构造函数私有化    
        private VerifyCodeHelper() { }        //创建单利对象资源并返回    
        public static VerifyCodeHelper GetSingleObj()       
         {          
           if (_VerifyCodeHelper == null)
            {                
                lock (_ObjLock)
                {                    
                    if (_VerifyCodeHelper == null)
                        _VerifyCodeHelper = new VerifyCodeHelper();
                }
            }           
            return _VerifyCodeHelper;
        }        #endregion

        #region 生产验证码  
        public enum VerifyCodeType 
        { 
            NumberVerifyCode, AbcVerifyCode, MixVerifyCode 
        };     

        /// <summary>  
        /// 1.数字验证码  
        /// </summary>  
        /// <param name="length"></param>  
        /// <returns></returns>  
        private string CreateNumberVerifyCode(int length)        
        {            
            int[] randMembers = new int[length];            
            int[] validateNums = new int[length];            
            string validateNumberStr = "";           
            //生成起始序列值    
            int seekSeek = unchecked((int)DateTime.Now.Ticks);
            Random seekRand = new Random(seekSeek);            
            int beginSeek = seekRand.Next(0, Int32.MaxValue - length * 10000);            
            int[] seeks = new int[length];            
            for (int i = 0; i < length; i++)
            {
                beginSeek += 10000;
                seeks[i] = beginSeek;
            }            
            //生成随机数字    
            for (int i = 0; i < length; i++)
            {
                Random rand = new Random(seeks[i]);                
                int pownum = 1 * (int)Math.Pow(10, length);
                randMembers[i] = rand.Next(pownum, Int32.MaxValue);
            }            
            //抽取随机数字    
            for (int i = 0; i < length; i++)
            {                
                string numStr = randMembers[i].ToString();                
                int numLength = numStr.Length;
                Random rand = new Random();                
                int numPosition = rand.Next(0, numLength - 1);
                validateNums[i] = Int32.Parse(numStr.Substring(numPosition, 1));
            }           
            //生成验证码    
            for (int i = 0; i < length; i++)
            {
                validateNumberStr += validateNums[i].ToString();
            }            
            return validateNumberStr;
        }
        /// <summary>  
        /// 2.字母验证码  
        /// </summary>  
        /// <param name="length">字符长度</param>  
        /// <returns>验证码字符</returns>  
        private string CreateAbcVerifyCode(int length)        
        {            
            char[] verification = new char[length];            
            char[] dictionary = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',                'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'
            };
            Random random = new Random();            
            for (int i = 0; i < length; i++)
            {
                verification[i] = dictionary[random.Next(dictionary.Length - 1)];
            }            
            return new string(verification);
        }       
        /// <summary>  
        /// 3.混合验证码  
        /// </summary>  
        /// <param name="length">字符长度</param>  
        /// <returns>验证码字符</returns>  
        private string CreateMixVerifyCode(int length)        
        {            
            char[] verification = new char[length];            
            char[] dictionary = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',                '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',                'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'
            };
            Random random = new Random();            
            for (int i = 0; i < length; i++)
            {
                verification[i] = dictionary[random.Next(dictionary.Length - 1)];
            }            
            return new string(verification);
        }        
        /// <summary>  
        /// 产生验证码（随机产生4-6位）  
        /// </summary>  
        /// <param name="type">验证码类型：数字，字符，符合</param>  
        /// <returns></returns>  
        public string CreateVerifyCode(VerifyCodeType type)        
        {            
            string verifyCode = string.Empty;
            Random random = new Random();            
            int length = 4;// random.Next(4, 6);
            switch (type)
            {                
                case VerifyCodeType.NumberVerifyCode:
                    verifyCode = GetSingleObj().CreateNumberVerifyCode(length);                    
                    break;                
                case VerifyCodeType.AbcVerifyCode:
                    verifyCode = GetSingleObj().CreateAbcVerifyCode(length);                    
                    break;                
                case VerifyCodeType.MixVerifyCode:
                    verifyCode = GetSingleObj().CreateMixVerifyCode(length);                   
                    break;
            }           
            return verifyCode;
        }        
        #endregion

        #region 验证码图片  
        /// <summary>  
        /// 验证码图片 => Bitmap  
        /// </summary>  
        /// <param name="verifyCode">验证码</param>  
        /// <param name="width">宽</param>  
        /// <param name="height">高</param>  
        /// <returns>Bitmap</returns>  
        public Bitmap CreateBitmapByImgVerifyCode(string verifyCode, int width, int height)        
        {
            Font font = new Font("Arial", 14, (FontStyle.Bold | FontStyle.Italic));
            Brush brush;
            Bitmap bitmap = new Bitmap(width, height);
            Graphics g = Graphics.FromImage(bitmap);
            SizeF totalSizeF = g.MeasureString(verifyCode, font);
            SizeF curCharSizeF;
            PointF startPointF = new PointF(0, (height - totalSizeF.Height) / 2);
            Random random = new Random(); //随机数产生器  
            g.Clear(Color.White); 
            //清空图片背景色    
            for (int i = 0; i < verifyCode.Length; i++)
            {
                brush = new LinearGradientBrush(new Point(0, 0), new Point(1, 1), Color.FromArgb(random.Next(255), random.Next(255), random.Next(255)), Color.FromArgb(random.Next(255), random.Next(255), random.Next(255)));
                g.DrawString(verifyCode[i].ToString(), font, brush, startPointF);
                curCharSizeF = g.MeasureString(verifyCode[i].ToString(), font);
                startPointF.X += curCharSizeF.Width;
            }            
            //画图片的干扰线    
            for (int i = 0; i < 10; i++)
            {                
                int x1 = random.Next(bitmap.Width);                
                int x2 = random.Next(bitmap.Width);                
                int y1 = random.Next(bitmap.Height);                
                int y2 = random.Next(bitmap.Height);
                g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
            }            
            //画图片的前景干扰点    
            for (int i = 0; i < 100; i++)
            {                
                int x = random.Next(bitmap.Width);                
                int y = random.Next(bitmap.Height);
                bitmap.SetPixel(x, y, Color.FromArgb(random.Next()));
            }

            g.DrawRectangle(new Pen(Color.Silver), 0, 0, bitmap.Width - 1, bitmap.Height - 1); //画图片的边框线    
            g.Dispose();            
            return bitmap;
        }        
        /// <summary>  
        /// 验证码图片 => byte[]  
        /// </summary>  
        /// <param name="verifyCode">验证码</param>  
        /// <param name="width">宽</param>  
        /// <param name="height">高</param>  
        /// <returns>byte[]</returns>  
        public byte[] CreateByteByImgVerifyCode(string verifyCode, int width, int height)        {
            Font font = new Font("Arial", 14, (FontStyle.Bold | FontStyle.Italic));
            Brush brush;
            Bitmap bitmap = new Bitmap(width, height);
            Graphics g = Graphics.FromImage(bitmap);
            SizeF totalSizeF = g.MeasureString(verifyCode, font);
            SizeF curCharSizeF;
            PointF startPointF = new PointF(0, (height - totalSizeF.Height) / 2);
            Random random = new Random(); //随机数产生器  
            g.Clear(Color.White); //清空图片背景色    
            for (int i = 0; i < verifyCode.Length; i++)
            {
                brush = new LinearGradientBrush(new Point(0, 0), new Point(1, 1), Color.FromArgb(random.Next(255), random.Next(255), random.Next(255)), Color.FromArgb(random.Next(255), random.Next(255), random.Next(255)));
                g.DrawString(verifyCode[i].ToString(), font, brush, startPointF);
                curCharSizeF = g.MeasureString(verifyCode[i].ToString(), font);
                startPointF.X += curCharSizeF.Width;
            }            
            //画图片的干扰线    
            for (int i = 0; i < 10; i++)
            {                
                int x1 = random.Next(bitmap.Width);                
                int x2 = random.Next(bitmap.Width);                
                int y1 = random.Next(bitmap.Height);                
                int y2 = random.Next(bitmap.Height);
                g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
            }            
            //画图片的前景干扰点    
            for (int i = 0; i < 100; i++)
            {                
                int x = random.Next(bitmap.Width);                
                int y = random.Next(bitmap.Height);
                bitmap.SetPixel(x, y, Color.FromArgb(random.Next()));
            }

            g.DrawRectangle(new Pen(Color.Silver), 0, 0, bitmap.Width - 1, bitmap.Height - 1); 
            //画图片的边框线    
            g.Dispose();            
            //保存图片数据    
            MemoryStream stream = new MemoryStream();
            bitmap.Save(stream, ImageFormat.Jpeg);            
            //输出图片流    
            return stream.ToArray();

        }        
        #endregion
    }
}

3、添加Controller

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Caching.Memory;
using System.DrawingCore.Imaging;
using System.IO;
using WoDian.Common.Core.Helper;

namespace WoDian.MVCBackstage.Core.Controllers
{
    public class VerifyCodeController : Controller
    {
        private IMemoryCache _cache;
        public VerifyCodeController(IMemoryCache memoryCache)
        {
            _cache = memoryCache;
        }
        public IActionResult Index()
        {
            return View();
        }
        /// <summary>  
        /// 数字验证码  
        /// </summary>  
        /// <returns></returns>  
        public FileContentResult NumberVerifyCode()
        {
            string code = VerifyCodeHelper.GetSingleObj().CreateVerifyCode(VerifyCodeHelper.VerifyCodeType.NumberVerifyCode);
            _cache.Set("yzm", code);
            byte[] codeImage = VerifyCodeHelper.GetSingleObj().CreateByteByImgVerifyCode(code, 80, 40);
            return File(codeImage, @"image/jpeg");
        }

        /// <summary>  
        /// 字母验证码  
        /// </summary>  
        /// <returns></returns>  
        public FileContentResult AbcVerifyCode()
        {
            string code = VerifyCodeHelper.GetSingleObj().CreateVerifyCode(VerifyCodeHelper.VerifyCodeType.AbcVerifyCode);
            var bitmap = VerifyCodeHelper.GetSingleObj().CreateBitmapByImgVerifyCode(code, 100, 40);
            MemoryStream stream = new MemoryStream();
            bitmap.Save(stream, ImageFormat.Png);
            return File(stream.ToArray(), "image/png");
        }

        /// <summary>  
        /// 混合验证码  
        /// </summary>  
        /// <returns></returns>  
        public FileContentResult MixVerifyCode()
        {
            string code = VerifyCodeHelper.GetSingleObj().CreateVerifyCode(VerifyCodeHelper.VerifyCodeType.MixVerifyCode);
            var bitmap = VerifyCodeHelper.GetSingleObj().CreateBitmapByImgVerifyCode(code, 100, 40);
            MemoryStream stream = new MemoryStream();
            bitmap.Save(stream, ImageFormat.Gif);
            return File(stream.ToArray(), "image/gif");
        }
    }
}

4、页面中添加调用

<div class="col-md-12">                
    <div class="form-group size-4">                   
                    <input class="required form-control "  name="CheckCode" placeholder="Code *" type="text" value="" style="width:70%">                    <img id="mixImg" title="Code" src="/Validation/NumberVerifyCode" alt="vcode" onclick="refresh()" style="cursor:pointer;" />             
    </div>            
 </div>

function refresh() 
{    
    var id = document.getElementById("mixImg");    
    var str = "/Validation/NumberVerifyCode?random=" + Math.random();
    id.setAttribute("src", str);
}

本地Windows 开发测试都是OK了

/*******************************注意***********************************/ 在部署到线上（针对线上是Linux服务器的可能会出现以下几种情况，大家注意了）

1.验证码图片显示不出来

那么按如下方式执行相关命令：

yum install autoconf automake libtool
yum install freetype-devel fontconfig libXft-devel
yum install libjpeg-turbo-devel libpng-devel giflib-devel libtiff-devel libexif-devel
yum install glib2-devel cairo-devel
git clone https://github.com/mono/libgdiplus
cd libgdiplus
./autogen.sh
make
make install
cd /usr/lib64/
ln -s /usr/local/lib/libgdiplus.so gdiplus.dll

运气好可能就正常，如果这些命令执行完还不行，那就要看是不是出现下面的问题：

2.验证码乱码的解决

这个主要是针对可以生成但是会出现乱码问题，说明是字体问题： 主要是解决字体问题。 在生成验证码的代码中， 关于字体的有一行：

string[] font = { "Times New Roman" };

所以先在  Windows 系统中找到：

复制到 Linux 中的 /usr/share/fonts/micro/ 下 mkdir /usr/share/fonts/micro/ cd /usr/share/fonts/micro/ # 字体文件复制到这个文件夹， 略 fc-cache  #重新加载字体 再重新执行 dotnet Web.dll , 验证码正常了 如果到这里正常了那么运气也是相当的好，可是不是所有人都有这么好运气，可能还会出现下面这种情况：

3.The type initializer for 'System.DrawingCore.GDIPlus' threw an exception

解决办法： centos上安装libgdiplus-devel； 命令如下：yum install libgdiplus-devel 安装完成后即可解决上面问题 好了，大功告成，以上都是我亲身测试出来的，网上的教程都是零零碎碎，我这边就针对会遇到的多种情况都总结一下，希望对大家有帮助吧。如果还有其他情况可以评论私聊我，一起加油，奥力给。