本文介绍生成C#验证码的方法，可将本方法放在一个 ashx 文件里，并继承自 System.Web.SessionState.IRequiresSessionState 以保存 session 。
using System;
using System.Drawing;
using System.Drawing.Drawing2D;
#region Create
private void Create(string code)
{
if (code == null || code.Trim() == String.Empty) return;
Bitmap image = new Bitmap((int)Math.Ceiling((code.Length * 11.5)), 21);
Graphics g = Graphics.FromImage(image);
try
{
Random random = new Random();
g.Clear(Color.White);
for (int i = 0; i < 25; 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, y1, x2, y2);
}
//Font font = new Font("Arial", 11, (FontStyle.Bold | FontStyle.Italic));
Font font = new Font("Arial", 11, (FontStyle.Regular | FontStyle.Bold));
LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
g.DrawString(code, font, brush, 2, 2);
font.Dispose();
brush.Dispose();
for (int i = 0; i < 100; 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), 0, 0, image.Width - 1, image.Height - 1);
System.IO.MemoryStream ms = new System.IO.MemoryStream();
image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
Response.ClearContent();
Response.ContentType = "image/Gif";
Response.BinaryWrite(ms.ToArray());
ms.Dispose();
}
finally
{
g.Dispose();
image.Dispose();
}
}
#endregion