.Net core验证码生成

首先，项目添加对ZKWeb.System.Drawing的引用；

生成验证码代码如下：

public class VierificationCodeServices
    {
        /// <summary>  
        /// 该方法用于生成指定位数的随机数  
        /// </summary>  
        /// <param name="VcodeNum">参数是随机数的位数</param>  
        /// <returns>返回一个随机数字符串</returns>  
        private string RndNum(int VcodeNum)
        {
            //验证码可以显示的字符集合  
            string vChar = "0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f,g,h,i,j,k,l,m,n,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,P,P,Q,R,S,T,U,V,W,X,Y,Z";
            string[] vcArray = vChar.Split(new Char[] { ',' });//拆分成数组   
            string code = "";//产生的随机数  
            int temp = -1;//记录上次随机数值，尽量避避免生产几个一样的随机数  

            Random rand = new Random();
            //采用一个简单的算法以保证生成随机数的不同  
            for (int i = 1; i < VcodeNum + 1; i++)
            {
                if (temp != -1)
                {
                    rand = new Random(i * temp * unchecked((int)DateTime.Now.Ticks));//初始化随机类  
                }
                int t = rand.Next(61);//获取随机数  
                if (temp != -1 && temp == t)
                {
                    return RndNum(VcodeNum);//如果获取的随机数重复，则递归调用  
                }
                temp = t;//把本次产生的随机数记录起来  
                code += vcArray[t];//随机数的位数加一  
            }
            return code;
        }

        /// <summary>  
        /// 该方法是将生成的随机数写入图像文件  
        /// </summary>  
        /// <param name="code">code是一个随机数</param>
        /// <param name="numbers">生成位数（默认4位）</param>  
        public MemoryStream Create(out string code, int numbers = 4)
        {
            code = RndNum(numbers);
            Bitmap img = null;
            Graphics g = null;
            MemoryStream ms = null;
            Random random = new Random();
            //验证码颜色集合  
            Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };

            //验证码字体集合
            string[] fonts = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体" };


            //定义图像的大小，生成图像的实例  
            img = new Bitmap((int)code.Length * 18, 32);

            g = Graphics.FromImage(img);//从Img对象生成新的Graphics对象    

            g.Clear(Color.White);//背景设为白色  

            //在随机位置画背景点  
            for (int i = 0; i < 100; i++)
            {
                int x = random.Next(img.Width);
                int y = random.Next(img.Height);
                g.DrawRectangle(new Pen(Color.LightGray, 0), x, y, 1, 1);
            }
            //验证码绘制在g中  
            for (int i = 0; i < code.Length; i++)
            {
                int cindex = random.Next(7);//随机颜色索引值  
                int findex = random.Next(5);//随机字体索引值  
                Font f = new Font(fonts[findex], 15, FontStyle.Bold);//字体  
                Brush b = new SolidBrush(c[cindex]);//颜色  
                int ii = 4;
                if ((i + 1) % 2 == 0)//控制验证码不在同一高度  
                {
                    ii = 2;
                }
                g.DrawString(code.Substring(i, 1), f, b, 3 + (i * 12), ii);//绘制一个验证字符  
            }
            ms = new MemoryStream();//生成内存流对象  
            img.Save(ms, ImageFormat.Jpeg);//将此图像以Png图像文件的格式保存到流中  

            //回收资源  
            g.Dispose();
            img.Dispose();
            return ms;
        }
    }

发布到CentOS中，需要安装libgdiplus：

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

 也可以这样安装：

yum install -y epel-release
yum whatprovides libgdiplus
yum install -y libgdiplus-2.10-9.el7.x86_64
yum install -y dejavu-fonts-common dejavu-lgc-sans-mono-fonts