/// <summary>
/// Creates a random text and initializes the CAPTCHA image.
/// </summary>
private void InitializeCaptcha()
{
string captchaText = GenerateCaptchaString();
HashedText = HashText(captchaText);
ServerImage.ImageUrl = "CaptchaImageHandler.ashx?text=" + HttpUtility.UrlEncode(CaptchaSecurity.Encrypt(captchaText));
}
/// <summary>
/// Enables processing of HTTP Web requests by a custom HttpHandler that implements the <see cref="T:System.Web.IHttpHandler"/> interface.
/// </summary>
/// <param name="context">An <see cref="T:System.Web.HttpContext"/> object that provides references to the intrinsic server objects (for example, Request, Response, Session, and Server) used to service HTTP requests.</param>
public void ProcessRequest(HttpContext context)
{
Random random = new Random();
// Create a Bitmap and setup brushes and text formatting to use.
Image bitmap = new Bitmap(200, 50);
Graphics graphic = Graphics.FromImage(bitmap);
Rectangle rect = new Rectangle(0, 0, bitmap.Width, bitmap.Height);
HatchBrush backgroundBrush = new HatchBrush(HatchStyle.SmallConfetti, Color.Gray, Color.White);
HatchBrush drawingBrush = new HatchBrush(HatchStyle.SmallConfetti, Color.Gray, Color.Black);
Pen thinPen = new Pen(drawingBrush);
Font font = new Font("Arial", 30, FontStyle.Bold);
StringFormat format = new StringFormat();
format.Alignment = StringAlignment.Center;
format.LineAlignment = StringAlignment.Center;
format.Trimming = StringTrimming.Word;
// Fill background of image
graphic.SmoothingMode = SmoothingMode.AntiAlias;
graphic.FillRectangle(backgroundBrush, rect);
// Get the text to draw.
string encryptedTextToDraw = context.Request.QueryString["text"];
string textToDraw = String.Empty;
if (!String.IsNullOrEmpty(encryptedTextToDraw))
{
textToDraw = CaptchaSecurity.Decrypt(encryptedTextToDraw);
}
// Create a path using the text and warp it randomly.
GraphicsPath path = new GraphicsPath();
path.AddString(textToDraw, font.FontFamily, (int)font.Style, font.Size, rect, format);
float warpfactor = 5; // The texts gets more distorted with higher warpfactor
PointF[] points =
{
new PointF(random.Next(rect.Width) / warpfactor, random.Next(rect.Height) / warpfactor),
new PointF(rect.Width - random.Next(rect.Width) / warpfactor, random.Next(rect.Height) / warpfactor),
new PointF(random.Next(rect.Width) / warpfactor, rect.Height - random.Next(rect.Height) / warpfactor),
new PointF(rect.Width - random.Next(rect.Width) / warpfactor, rect.Height - random.Next(rect.Height) / warpfactor)
};
path.Warp(points, rect);
graphic.FillPath(drawingBrush, path);
// Fill the image with random dots.
int m = Math.Max(rect.Width, rect.Height);
for (int i = 0; i < (int)(rect.Width * rect.Height / 30); i++)
{
graphic.FillEllipse(drawingBrush, random.Next(rect.Width), random.Next(rect.Height), random.Next(m / 50), random.Next(m / 50));
}
// Fill the image with random lines.
for (int i = 0; i < 8; i++)
{
graphic.DrawBezier(thinPen,
new Point(random.Next(rect.Width), random.Next(rect.Height)),
new Point(random.Next(rect.Width), random.Next(rect.Height)),
new Point(random.Next(rect.Width), random.Next(rect.Height)),
new Point(random.Next(rect.Width), random.Next(rect.Height))
);
}
context.Response.Clear();
context.Response.ContentType = "image/jpg";
bitmap.Save(context.Response.OutputStream, ImageFormat.Jpeg);
// Make sure we release all drawing resources
bitmap.Dispose();
graphic.Dispose();
thinPen.Dispose();
backgroundBrush.Dispose();
drawingBrush.Dispose();
font.Dispose();
format.Dispose();
path.Dispose();
context.Response.End();
}