生成图片验证码（.NET）

一、生成随机字符串

　方法一：

        public string CreateRandomCode(int codeCount)
        {
            string allChar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,a,b,c,d,e,f,g,h,i,g,k,l,m,n,o,p,q,r,F,G,H,I,G,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,s,t,u,v,w,x,y,z";
            string[] allCharArray = allChar.Split(',');
            string randomCode = "";     //声明随机字符串变量
            int temp = -;
            Random rand = new Random();     //声明随机数对象
            for (int i = ; i < codeCount; i++)
            {
                if (temp != -)
                {
                    rand = new Random(i * temp * ((int)DateTime.Now.Ticks));
                }
                int t = rand.Next();
                if (temp == t)
                {
                    return CreateRandomCode(codeCount);
                }
                temp = t;
                randomCode += allCharArray[t];
            }
            return randomCode;
        }

　方法二：

        private static string GetRandomString(int length)
        {
            return Guid.NewGuid().ToString("N").Substring(( - length), length);
        }

二、创建验证码图片

　实现方法一：

public byte[] CreateValidateGraphic(string validateCode)
        {
            //声明用于处理由像素数据定义的图像的对象（宽，高）
            Bitmap image = new Bitmap((int)Math.Ceiling(validateCode.Length * 16.0), );

            Graphics g = Graphics.FromImage(image);
            try
            {
                Random random = new Random();

                g.Clear(Color.White);       //清空图片背景色

                //画图片的干扰线
                for (int i = ; i < ; i++)
                {
                    int x1 = random.Next(image.Width);
                    int x2 = random.Next(image.Width);
                    int y1 = random.Next(image.Height);
                    int y2 = random.Next(image.Height);
                    g.DrawLine(new Pen(Color.Silver), x1, x2, y1, y2);
                }

                Font font = new Font("Arial", , (FontStyle.Bold | FontStyle.Italic));     //设置字体样式和大小
                LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(, , image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
                g.DrawString(validateCode, font, brush, , );          //绘制指定的字符串

                //画图片的前景干扰线
                for (int i = ; i < ; i++)
                {
                    int x = random.Next(image.Width);
                    int y = random.Next(image.Height);
                    image.SetPixel(x, y, Color.FromArgb(random.Next()));
                }

                g.DrawRectangle(new Pen(Color.Silver), , , image.Width - , image.Height - );        //画图片的边框线

                //保存图片数据
                MemoryStream stream = new MemoryStream();
                image.Save(stream, ImageFormat.Jpeg);

                //输出图片流
                return stream.ToArray();
            }
            finally
            {
                g.Dispose();
                image.Dispose();
            }
        }

　实现方法二：

        /// <summary>
        /// 由随机字符串，随即颜色背景，和随机线条产生的Image
        /// </summary>
        /// <returns>Image</returns>
        public static byte[] GetVcodeImg(string text, int width = , int height = , int fontSize = )
        //返回 Image
        {
            int charNum = text.Length;
            //声明一个位图对象
            Bitmap bitMap = null;
            //声明一个绘图画面
            Graphics gph = null;
            //创建内存流
            MemoryStream memStream = new MemoryStream();
            Random random = new Random();
            //由给定的需要生成字符串中字符个数 CharNum， 图片宽度 Width 和高度 Height 确定字号 FontSize，
            //确保不因字号过大而不能全部显示在图片上
            int fontWidth = (int)Math.Round(width / (charNum + ) / 1.3);
            int fontHeight = (int)Math.Round(height / 1.5);
            //字号取二者中小者，以确保所有字符能够显示，并且字符的下半部分也能显示
            fontSize = fontWidth <= fontHeight ? fontWidth : fontHeight;
            //创建位图对象
            bitMap = new Bitmap(width + fontSize, height);
            //根据上面创建的位图对象创建绘图图面
            gph = Graphics.FromImage(bitMap);
            //设定验证码图片背景色
            gph.Clear(GetControllableColor());
            //产生随机干扰线条
            for (int i = ; i < ; i++)
            {
                Pen backPen = new Pen(GetControllableColor(), );
                //线条起点
                int x = random.Next(width);
                int y = random.Next(height);
                //线条终点
                int x2 = random.Next(width);
                int y2 = random.Next(height);
                //划线
                gph.DrawLine(backPen, x, y, x2, y2);
            }
            //定义一个含10种字体的数组
            String[] fontFamily =
            {
                "Arial", "Verdana", "Comic Sans MS", "Impact", "Haettenschweiler",
                "Lucida Sans Unicode", "Garamond", "Courier New", "Book Antiqua", "Arial Narrow"
            };

            SolidBrush sb = new SolidBrush(GetControllableColor());
            //通过循环,绘制每个字符,
            for (int i = ; i < text.Length; i++)
            {
                Font textFont = new Font(fontFamily[random.Next()], fontSize, FontStyle.Bold); //字体随机,字号大小30,加粗
                //每次循环绘制一个字符,设置字体格式,画笔颜色,字符相对画布的X坐标,字符相对画布的Y坐标
                int space = (int)Math.Round((double)((width - fontSize * (charNum + )) / charNum));
                //纵坐标
                int y = (int)Math.Round((double)((height - fontSize) / ));
                gph.DrawString(text.Substring(i, ), textFont, sb, fontSize + i * (fontSize + space), y);
            }
            //扭曲图片
            bitMap = TwistImage(bitMap, true, random.Next(, ), random.Next());

            bitMap.Save(memStream, ImageFormat.Gif);

            bitMap.Dispose();

            return memStream.ToArray();
        }

        /// <summary>
        /// 产生一种 R,G,B 均大于 colorBase 随机颜色，以确保颜色不会过深
        /// </summary>
        /// <returns>背景色</returns>
        private static Color GetControllableColor(int colorBase)
        {
            Color color = Color.Black;

            Random random = new Random();
            //确保 R,G,B 均大于 colorBase，这样才能保证背景色较浅
            color = Color.FromArgb(random.Next() + colorBase, random.Next() + colorBase, random.Next() + colorBase);
            return color;
        }

        /// <summary>
        /// 扭曲图片
        /// </summary>
        /// <param name="srcBmp"></param>
        /// <param name="bXDir"></param>
        /// <param name="dMultValue"></param>
        /// <param name="dPhase"></param>
        /// <returns></returns>
        private static Bitmap TwistImage(Bitmap srcBmp, bool bXDir, double dMultValue, double dPhase)
        {
            int leftMargin = ;
            int rightMargin = ;
            int topMargin = ;
            int bottomMargin = ;

            float PI2 = 6.28318530717959f;
            Bitmap destBmp = new Bitmap(srcBmp.Width, srcBmp.Height);
            double dBaseAxisLen = bXDir ? Convert.ToDouble(destBmp.Height) : Convert.ToDouble(destBmp.Width);
            for (int i = ; i < destBmp.Width; i++)
            {
                for (int j = ; j < destBmp.Height; j++)
                {
                    double dx = ;
                    dx = bXDir ? PI2 * Convert.ToDouble(j) / dBaseAxisLen : PI2 * Convert.ToDouble(i) / dBaseAxisLen;
                    dx += dPhase;
                    double dy = Math.Sin(dx);
                    //取得当前点的颜色
                    int nOldX = ;
                    int nOldY = ;
                    nOldX = bXDir ? i + Convert.ToInt32(dy * dMultValue) : i;
                    nOldY = bXDir ? j : j + Convert.ToInt32(dy * dMultValue);
                    var color = srcBmp.GetPixel(i, j);
                    if (nOldX >= leftMargin && nOldX < destBmp.Width - rightMargin && nOldY >= bottomMargin &&
                        nOldY < destBmp.Height - topMargin)
                    {
                        destBmp.SetPixel(nOldX, nOldY, color);
                    }
                }
            }
            return destBmp;
        }

三、将 8位字节数组 转换为 base64字符串 类型的数据

        private String BytesToBase64(Byte[] bytes)
        {
            try
            {
                return Convert.ToBase64String(bytes);
            }
            catch
            {
                return null;
            }
        }

四、接口与调用

　　本例是在网站中通过 ashx 文件写的

调用以上三个方法：

        public void ProcessRequest(HttpContext context)
        {
            context.Response.ContentType = "text/plain";
            StrHelper sh = new StrHelper(context);　　　　//自己写的类，这里用来返回json数据

            string code = CreateRandomCode(); 　　　　　　//验证码的字符为4个
            string image = BytesToBase64(CreateValidateGraphic(code));　　　　//将图片验证码用base64类型的字符串返回（便于前端显示）
            sh.RebackJson(new { status = , code = code, image = image, type = "image/Jpeg" });
        }

在页面中调用：

<a >
    <img id="img1" src="" onclick="changeImage()"/>
</a>
<script src="~/Scripts/jquery-1.10.2.js"></script>
<script>
    window.onload = function () {
        changeImage();
    }
    function changeImage() {
        $.ajax({
            url: "http://服务器地址:端口号/SecurityCode.ashx",
            type: "post",
            success: function (data) {
                data = JSON.parse(data);

                console.log(data);
                $("#img1").attr("src", 'data:image/png;base64,' + data.image);
            },
            error: function (data) { },
        })
    }
</script>

实现方式二 -- 存储到 Redis 缓存中

        /// <summary>
        /// 生成验证码
        /// </summary>
        /// <returns></returns>
        public static async Task<VCode_Return> GetCodeAsync()
        {
            //生成数字并保存，将和图片的base64返回
            var text = GetRandomString();

             string vid = ObjectId.GenerateNewId().ToString();

            //存储缓存
            await Redis.TopOauth.StringSetAsync($"VCODE:{vid}", text.ToLower(), new TimeSpan(, , ));

            var bytes = GetVcodeImg(text);
            //生成图片
            string imgbase64 = Convert.ToBase64String(bytes);
            //返回验证码
            VCode_Return myReturn = new VCode_Return { vcode_image = imgbase64, vcodeid = vid };
            return myReturn;
        }

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