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()
        {

            .......
        }