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This article introduces the relevant knowledge of "how to write ASP.NET to achieve dynamic GIF CAPTCHA". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Implementation method:

Public void ShowCode () {/ / object instantiation Validate GifValidate = new Validate (); # region sets the CAPTCHA (if not set, it will be generated by default) / / the number of CAPTCHA digits, not less than 4 digits GifValidate.ValidateCodeCount = 4; / / CAPTCHA font model (default 13) GifValidate.ValidateCodeSize = 13 / / CAPTCHA picture height, the higher the height, the more obvious the upper and lower offset of the characters GifValidate.ImageHeight = 23; / / CAPTCHA character and line color (need to refer to color class) GifValidate.DrawColor = System.Drawing.Color.BlueViolet; / / CAPTCHA font (need to fill in the font installed by server) GifValidate.ValidateCodeFont = "Arial" / / whether the character of the CAPTCHA is anti-aliased GifValidate.FontTextRenderingHint = false; / / defines all the characters in the CAPTCHA ("," separation). It seems that Chinese GifValidate.AllChar = "1, 2, 3, 4, 5, 6, 8, 8, 9, 0, 0, 0, 0, 0, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8 # endregion / / output image (Session name) GifValidate.OutPutValidate ("GetCode");}

Call the main method:

Public class Validate {public string AllChar = "1, Color.BlueViolet; public bool FontTextRenderingHint 2, 4, 5, 6, 7, 7, 9, 0, 0, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 7, 7, 9, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, Public float ValidateCodeSize = 13f; private void CreateImageBmp (out Bitmap ImageFrame) {char [] chArray = this.ValidateCode.ToCharArray (0, this.ValidateCodeCount); int width = (int) ((this.TrueValidateCodeCount * this.ValidateCodeSize) * 1.3) + 4.0); ImageFrame = new Bitmap (width, this.ImageHeight); Graphics graphics = Graphics.FromImage (ImageFrame); graphics.Clear (Color.White) Font font = new Font (this.ValidateCodeFont, this.ValidateCodeSize, FontStyle.Bold); Brush brush = new SolidBrush (this.DrawColor); int maxValue = (int) Math.Max ((float) ((this.ImageHeight-this.ValidateCodeSize)-3f), (float) 2f); Random random = new Random (); for (int I = 0; I)

< this.TrueValidateCodeCount; i++) { int[] numArray = new int[] { (((int) (i * this.ValidateCodeSize)) + random.Next(1)) + 3, random.Next(maxValue) }; Point point = new Point(numArray[0], numArray[1]); if (this.FontTextRenderingHint) { graphics.TextRenderingHint = TextRenderingHint.SingleBitPerPixel; } else { graphics.TextRenderingHint = TextRenderingHint.AntiAlias; } graphics.DrawString(chArray[i].ToString(), font, brush, (PointF) point); } graphics.Dispose(); } private void CreateImageGif() { AnimatedGifEncoder encoder = new AnimatedGifEncoder(); MemoryStream stream = new MemoryStream(); encoder.Start(); encoder.SetDelay(5); encoder.SetRepeat(0); for (int i = 0; i < 10; i++) { Bitmap bitmap; this.CreateImageBmp(out bitmap); this.DisposeImageBmp(ref bitmap); bitmap.Save(stream, ImageFormat.Png); encoder.AddFrame(Image.FromStream(stream)); stream = new MemoryStream(); } encoder.OutPut(ref stream); HttpContext.Current.Response.ClearContent(); HttpContext.Current.Response.ContentType = "image/Gif"; HttpContext.Current.Response.BinaryWrite(stream.ToArray()); stream.Close(); stream.Dispose(); } private void CreateValidate() { this.ValidateCode = ""; string[] strArray = this.AllChar.Split(new char[] { ',' }); int index = -1; Random random = new Random(); for (int i = 0; i < this.ValidateCodeCount; i++) { if (index != -1) { random = new Random((i * index) * ((int) DateTime.Now.Ticks)); } int num3 = random.Next(0x23); if (index == num3) { this.CreateValidate(); } index = num3; this.ValidateCode = this.ValidateCode + strArray[index]; } if (this.ValidateCode.Length >

This.TrueValidateCodeCount) {this.ValidateCode = this.ValidateCode.Remove (this.TrueValidateCodeCount);}} private void DisposeImageBmp (ref Bitmap ImageFrame) {Graphics graphics = Graphics.FromImage (ImageFrame); Pen pen = new Pen (this.DrawColor, 1f); Random random = new Random (); Point [] pointArray = new Point [2]; for (int I = 0; I

< 15; i++) { pointArray[0] = new Point(random.Next(ImageFrame.Width), random.Next(ImageFrame.Height)); pointArray[1] = new Point(random.Next(ImageFrame.Width), random.Next(ImageFrame.Height)); graphics.DrawLine(pen, pointArray[0], pointArray[1]); } graphics.Dispose(); } public void OutPutValidate(string ValidateCodeSession) { this.CreateValidate(); this.CreateImageGif(); HttpContext.Current.Session[ValidateCodeSession] = this.ValidateCode; } public byte ValidateCodeCount { get { return this.TrueValidateCodeCount; } set { if (value >

4) {this.TrueValidateCodeCount = value;}

Verification code effect:

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