asp.Netはどのようにピクチャーの上で透かしの文字をプラスします

サイトの画像の著作権性とネット普及の可能性を保証するために、サイトの画像に会社名の透かしを付ける必要があるお客様もいるかもしれません.次のコードは、画像に透かし文字を付ける方法を紹介します.
 
最初のステップでは、ImageHandlerという一般的なハンドラを追加します.

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Net.Mime;
using System.IO;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;

/// <summary>
/// Summary description for ImageHandler
/// </summary>
public class ImageHandler : IHttpHandler
{
    public ImageHandler()
    {
    }

    public string GetContentType(String path)
    {
        switch (Path.GetExtension(path))
        {
            case ".bmp": return "Image/bmp";
            case ".gif": return "Image/gif";
            case ".jpg": return "Image/jpeg";
            case ".png": return "Image/png";
            default: break;
        }
        return String.Empty;
    }

    public ImageFormat GetImageFormat(String path)
    {
        switch (Path.GetExtension(path).ToLower())
        {
            case ".bmp": return ImageFormat.Bmp;
            case ".gif": return ImageFormat.Gif;
            case ".jpg": return ImageFormat.Jpeg;
            case ".png": return ImageFormat.Png;
            default: return null;
        }
    }

    protected byte[] WatermarkImage(HttpContext context)
    {

        byte[] imageBytes = null;
        if (File.Exists(context.Request.PhysicalPath))
        {
            // Normally you'd put this in a config file somewhere.
            string watermark = "    ";

            Image image = Image.FromFile(context.Request.PhysicalPath);

            Graphics graphic;
            if (image.PixelFormat != PixelFormat.Indexed && image.PixelFormat != PixelFormat.Format8bppIndexed && image.PixelFormat != PixelFormat.Format4bppIndexed && image.PixelFormat != PixelFormat.Format1bppIndexed)
            {
                // Graphic is not a Indexed (GIF) image
                graphic = Graphics.FromImage(image);
            }
            else
            {
                /* Cannot create a graphics object from an indexed (GIF) image. 
                 * So we're going to copy the image into a new bitmap so 
                 * we can work with it. */
                Bitmap indexedImage = new Bitmap(image);
                graphic = Graphics.FromImage(indexedImage);

                // Draw the contents of the original bitmap onto the new bitmap. 
                graphic.DrawImage(image, 0, 0, image.Width, image.Height);
                image = indexedImage;
            }
            graphic.SmoothingMode = SmoothingMode.AntiAlias & SmoothingMode.HighQuality;

            Font myFont = new Font("Arial", 15);
            SolidBrush brush = new SolidBrush(Color.FromArgb(255, Color.Red));

            /* This gets the size of the graphic so we can determine 
             * the loop counts and placement of the watermarked text. */
            SizeF textSize = graphic.MeasureString(watermark, myFont);

            //// Write the text across the image. 
            //for (int y = 0; y < image.Height; y++)
            //{
            //    for (int x = 0; x < image.Width; x++)
            //    {
            //        PointF pointF = new PointF(x, y);
            //        graphic.DrawString(watermark, myFont, brush, pointF);
            //        x += Convert.ToInt32(textSize.Width);
            //    }
            //    y += Convert.ToInt32(textSize.Height);
            //}


            // Write the text at the right bottom of the image. 
            for (int y = image.Height-25; y < image.Height; y++)
            {
                for (int x = image.Width-100; x < image.Width; x++)
                {
                    PointF pointF = new PointF(x, y);
                    graphic.DrawString(watermark, myFont, brush, pointF);
                    x += Convert.ToInt32(textSize.Width);
                }
                y += Convert.ToInt32(textSize.Height);
            }

            using (MemoryStream memoryStream = new MemoryStream())
            {
                image.Save(memoryStream, GetImageFormat(context.Request.PhysicalPath));
                imageBytes = memoryStream.ToArray();
            }

        }
        return imageBytes;
    }

    #region IHttpHandler Members

    public bool IsReusable
    {
        get { return false; }
    }

    public void ProcessRequest(HttpContext context)
    {
        context.Response.Clear();
        context.Response.ContentType = GetContentType(context.Request.PhysicalPath);
        byte[] imageBytes = WatermarkImage(context);
        if (imageBytes != null)
        {
            context.Response.OutputStream.Write(imageBytes, 0, imageBytes.Length);
        }
        else
        {
            // No bytes = no image which equals NO FILE.    
            // Therefore send a 404 - not found response. 
            context.Response.StatusCode = 404;
        }
        context.Response.End();
    }

    #endregion
}

2つ目はwebですconfigには次のコードが追加されています.

    <httpHandlers>
      <!--<add verb="GET" type="ImageHandler" path="*.jpg,*.png,*.gif,*.bmp"/>-->
      <add verb="GET" type="ImageHandler" path="Uploads/*/*.jpg"/>      
    </httpHandlers>

ステップ3では、各ピクチャの右下隅に赤い「世復検出」の4文字を表示するようにデバッグします.