What is the method of this encoding?

[COLOR=#000000]<%@ WebHandler Language="C#" Class="GetImgText" %>[/COLOR]/*

Scrambled text generator.
Developed by: Aref Karimi
Email: [email protected]
Last update: 20 October 2009

This code is free to use. 
 
*/
using System;
using System.Web;
using System.Collections.Generic;
using System.Drawing;

public class GetImgText : IHttpHandler {
    
    public void ProcessRequest (HttpContext context) {
        context.Response.ContentType = "image/jpeg";
        var CaptchaText = SecurityHelper.DecryptString(
            Convert.FromBase64String(context.Request.QueryString["CaptchaText"]));
        if (CaptchaText != null)
        {
            List<Letter> letter = new List<Letter>();
            int TotalWidth = 0;
            int MaxHeight = 0;
            foreach (char c in CaptchaText)
            {
                var ltr = new Letter(c);
                letter.Add(ltr);
                int space = (new Random()).Next(5) + 1;
                ltr.space = space;
                System.Threading.Thread.Sleep(1);
                TotalWidth += ltr.LetterSize.Width+space;
                if (MaxHeight < ltr.LetterSize.Height)
                    MaxHeight = ltr.LetterSize.Height;
                System.Threading.Thread.Sleep(1);
            }
            const int HMargin = 5;
            const int VMargin = 3;

            Bitmap bmp = new Bitmap(TotalWidth + HMargin, MaxHeight + VMargin);
            var Grph = Graphics.FromImage(bmp);
            Grph.FillRectangle(new SolidBrush(Color.Lavender), 0, 0, bmp.Width, bmp.Height);
            Pixelate(ref bmp);
            Grph.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
            Grph.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            int xPos = HMargin;
            foreach (var ltr in letter)
            {
                Grph.DrawString(ltr.letter.ToString(), ltr.font, new SolidBrush(Color.Navy), xPos, VMargin );
                xPos += ltr.LetterSize.Width + ltr.space;
            }
            
            bmp.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
        }
    }
 
    public bool IsReusable {
        get {
            return false;
        }
    }
    private void Pixelate(ref Bitmap bmp)
    {
        Color[] Colors = { Color.Gray , Color.Red, Color.Blue, Color.Olive };
        for (int i = 0; i < 200; i++)
        {
            var rnd = new Random(DateTime.Now.Millisecond);
            var grp = Graphics.FromImage(bmp);
            Image background = Image.FromFile(HttpContext.Current.Server.MapPath("~/images/captcha/captcha3.jpg"));
            grp.DrawImage(background, new Rectangle(0, 0, bmp.Width, bmp.Height));
        }
    }
 [COLOR=#000000]}[/COLOR]