<%@ WebHandler Language="C#" Class="dynimage" %>

using System;
using System.Web;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
public class dynimage : IHttpHandler
{

    public void ProcessRequest(HttpContext context)
    {

        string imagetype = context.Request.QueryString["t"];
        switch (imagetype)
        {
            case "flag":
                {

                    Bitmap source = new Bitmap(context.Server.MapPath("~/graphics/FlagBlack16.png"));

                    int ARGB = int.Parse(context.Request.QueryString["argb"]);
                    Color NewColor = Color.FromArgb(ARGB);
                    swapcolor(Color.FromArgb(255, 0, 0, 0), NewColor, source);

                    context.Response.Clear();
                    context.Response.ContentType = "image/png";

                    using (MemoryStream stream = new MemoryStream())
                    {
                        source.Save(stream, ImageFormat.Png);

                        stream.WriteTo(context.Response.OutputStream);
                    }


                }
                break;
        }
    }


    public bool IsReusable {get{return false;}}
    protected void swapcolor(Color oldColor, Color newColor, Bitmap baseImage)
    {
        if (newColor != oldColor)
        {

            int width = baseImage.Width;
            int height = baseImage.Height;

            int i, j;
            for (i = 0; i < width; i++)
            {
                for (j = 0; j < height; j++)
                {
                    Color pixelColor = baseImage.GetPixel(i, j);

                    //Replace each all black pixel with the chosen color
                    if (pixelColor == oldColor)
                    {
                        baseImage.SetPixel(i, j, newColor);

                    }
                }
            }
        }
    }
}