Asp.net(C#)实现验证码功能

新建一个专门用来创建验证码图片的页面ValidateCode.aspx
它的后台cs文件代码如下：
PageLoad

private void Page_Load(object sender, System.EventArgs e)
        {
            string checkCode = CreateRandomCode(4);
            Session["CheckCode"] = checkCode;
            CreateImage(checkCode);
        }
 
其中CreateRandomCode是自定义的函数，参数代表验证码位数

private string CreateRandomCode(int codeCount)
        {
            string allChar = "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,W,X,Y,Z" ;
            string[] allCharArray = allChar.Split(',');
            string randomCode = "";
            int temp = -1;

            Random rand = new Random();
            for(int i = 0; i < codeCount; i++)
            {
                if(temp != -1)
                {
                    rand = new Random(i*temp*((int)DateTime.Now.Ticks));
                }
                int t = rand.Next(35);
                if(temp == t)
                {
                    return CreateRandomCode(codeCount);
                }
                temp = t;
                randomCode += allCharArray[t];
            }
            return randomCode;
        }
CreateImage也是一个自定义的函数，用于生成图

private void CreateImage(string checkCode)
        {
            int iwidth = (int)(checkCode.Length * 11.5);
            System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 20);
            Graphics g = Graphics.FromImage(image);
            Font f = new System.Drawing.Font("Arial", 10, System.Drawing.FontStyle.Bold);
            Brush b = new System.Drawing.SolidBrush(Color.White);
            //g.FillRectangle(new System.Drawing.SolidBrush(Color.Blue),0,0,image.Width, image.Height);
            g.Clear(Color.Blue);
            g.DrawString(checkCode, f, b, 3, 3);

            Pen blackPen = new Pen(Color.Black, 0);
            Random rand = new Random();
            for (int i=0;i<5;i++)
            {
                int y = rand.Next(image.Height);
                g.DrawLine(blackPen,0,y,image.Width,y);
            }
           
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            image.Save(ms,System.Drawing.Imaging.ImageFormat.Jpeg);
            Response.ClearContent();
            Response.ContentType = "image/Jpeg";
            Response.BinaryWrite(ms.ToArray());
            g.Dispose();
            image.Dispose();
        }

在需要用到验证码的页面添加一个控件即可，但是要把ImageUrl指向生成验证码的页面

<asp:Image Runat="server" ID="ImageCheck" ImageUrl="ValidateCode.aspx">asp:Image>