C#实现动态验证码生成与显示

public void setImage() 
        {
            string str = CreateRandomNum(5);
            CreateImage(str);
            //MessageBox.Show(str);
            pictureBox1.ImageLocation = "C:/Users/Administrator/Desktop/image/yanzhengma.gif";
        }

        public string CreateRandomNum(int NumCount) 
        {
            string allChar = "1,2,3,4,5,6,7,8,9,0,q,w,e,r,t,y,u,i,o,p,a,s,d,f,g,h,j,k,l,z,x,c,v,b,n,m";
            string[] allCharArray = allChar.Split(',');
            string randomNum = "";
            int temp = -1;
            Random rand = new Random();
            for (int i = 0; i < NumCount;i++ )
            {
                if (temp != -1) 
                {
                    rand = new Random(i*temp*((int)DateTime.Now.Ticks));
                }
                int t = rand.Next(35);
                if (temp == t) 
                {
                    return CreateRandomNum(NumCount);
                }
                temp = t;
                randomNum += allCharArray[t];
            }
            return randomNum;