C# 图像验证码的实现

原文链接：http://dev.mjxy.cn/a-170.aspx

// Captcha Image

public class CaptchaImage
{
// Public properties (all read-only).
public string Text
{
get { return this.text; }
}
public Bitmap Image
{
get { return this.image; }
}
public int Width
{
get { return this.width; }
}
public int Height
{
get { return this.height; }
}

// Internal properties.
private string text;
private int width;
private int height;
private string familyName;
private Bitmap image;

// For generating random numbers.
private Random random = new Random();

// ====================================================================
// Initializes a new instance of the CaptchaImage class using the
// specified text, width and height.
// ====================================================================
public CaptchaImage(int length, int width, int height) : this(length, width, height, null)
{
}

// ====================================================================
// Initializes a new instance of the CaptchaImage class using the
// specified text, width, height and font family.
// ====================================================================
public CaptchaImage(int length, int width, int height, string familyName)
{
this.text = GenerateRandomText(length);
this.SetDimensions(width, height);
this.SetFamilyName(familyName);
this.GenerateImage();
}

private string GenerateRandomText(int length)
{
Random rnd = new Random();
List<char> table = new List<char>();

for (char i = 'A'; i <= 'Z'; i++)
table.Add(i);

for (char i = '0'; i <= '9'; i++)
table.Add(i);

string retVal = "";

for (int i = 0; i < length; i++)
retVal += table[rnd.Next(table.Count)];

return retVal;
}

// ====================================================================
// This member overrides Object.Finalize.
// ====================================================================
~CaptchaImage()
{
Dispose(false);
}

// ====================================================================
// Releases all resources used by this object.
// ====================================================================
public void Dispose()
{
GC.SuppressFinalize(this);
this.Dispose(true);
}

// ====================================================================
// Custom Dispose method to clean up unmanaged resources.
// ====================================================================
protected virtual void Dispose(bool disposing)
{
if (disposing)
// Dispose of the bitmap.
this.image.Dispose();
}

// ====================================================================
// Sets the image width and height.
// ====================================================================
private void SetDimensions(int width, int height)
{
// Check the width and height.
if (width <= 0)
throw new ArgumentOutOfRangeException("width", width, "Argument out of range, must be greater than zero.");
if (height <= 0)
throw new ArgumentOutOfRangeException("height", height, "Argument out of range, must be greater than zero.");
this.width = width;
this.height = height;
}

// ====================================================================
// Sets the font used for the image text.
// ====================================================================
private void SetFamilyName(string familyName)
{
// If the named font is not installed, default to a system font.
try
{
Font font = new Font(this.familyName, 12F);
this.familyName = familyName;
font.Dispose();
}
catch (Exception ex)
{
this.familyName = System.Drawing.FontFamily.GenericSerif.Name;
}
}

// ====================================================================
// Creates the bitmap image.
// ====================================================================
private void GenerateImage()
{

.......
}