登陆算数验证码，后台验证，相对前台验证更安全

本文主要是介绍登陆算数验证码，后台验证，相对前台验证更安全，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

前台：

    <div class="form-group verificationcode"><img style="width: 140px; vertical-align: middle;margin: auto;" /></div>$(".verificationcode img").on('click', function () {$(this).attr('src', '/RIPSP/Base/Account/GetVerificationImg?w=150&h=32&t=' + new Date());}).click();

后台：

        public object GetVerificationImg(int w, int h){string randomcode = GetVerificationCode();int randAngle = 30; //随机转动角度Bitmap map = new Bitmap(w, h);//创建图片背景Graphics graph = Graphics.FromImage(map);graph.Clear(Color.AliceBlue);//清除画面，填充背景graph.DrawRectangle(new Pen(Color.Black, 0), 0, 0, map.Width - 1, map.Height - 1);//画一个边框//graph.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;//模式Random rand = new Random();//背景噪点生成Pen blackPen = new Pen(Color.LightGray, 0);for (int i = 0; i < 50; i++){int x = rand.Next(0, map.Width);int y = rand.Next(0, map.Height);graph.DrawRectangle(blackPen, x, y, 1, 1);}//验证码旋转，防止机器识别char[] chars = randomcode.ToCharArray();//拆散字符串成单字符数组//文字距中StringFormat format = new StringFormat(StringFormatFlags.NoClip);format.Alignment = StringAlignment.Center;format.LineAlignment = StringAlignment.Center;//定义颜色Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };//定义字体string[] font = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体" };int cindex = rand.Next(7);for (int i = 0; i < chars.Length; i++){int findex = rand.Next(5);Font f = new System.Drawing.Font(font[findex], 14, System.Drawing.FontStyle.Bold);//字体样式(参数2为字体大小)Brush b = new System.Drawing.SolidBrush(c[cindex]);Point dot = new Point(14, 14);//graph.DrawString(dot.X.ToString(),fontstyle,new SolidBrush(Color.Black),10,150);//测试X坐标显示间距的float angle = rand.Next(-randAngle, randAngle);//转动的度数graph.TranslateTransform(dot.X, dot.Y);//移动光标到指定位置graph.RotateTransform(angle);graph.DrawString(chars[i].ToString(), f, b, 1, 1, format);//graph.DrawString(chars[i].ToString(),fontstyle,new SolidBrush(Color.Blue),1,1,format);graph.RotateTransform(-angle);//转回去graph.TranslateTransform(-2, -dot.Y);//移动光标到指定位置，每个字符紧凑显示，避免被软件识别}//生成图片System.IO.MemoryStream ms = new System.IO.MemoryStream();map.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);HttpContext.Current.Response.ClearContent();HttpContext.Current.Response.ContentType = "image/gif";HttpContext.Current.Response.BinaryWrite(ms.ToArray());graph.Dispose();map.Dispose();return null;}private string GetVerificationCode(){Random rand = new Random();int a = rand.Next(1, 99);int b = rand.Next(1, 100 - a);int c = a + b;HttpContext.Current.Session["loginyzm"] = c.ToString();return string.Format("{0} 加 {1} =?", a, b);}