asp.net如何在图片上加水印文字

为了保证网站图片的版权性和网络推广的可能性，有的客户可能需要在网站的图片上加上公司名称的水印。下面的代码就是介绍如何在图片上加上水印文字。

第一步，添加一个一般处理程序（Handler）,本例是ImageHandler

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 = "世复检测";

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
}

第二步，在web.config里添加如下代码：

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

第三步，调试在每一个图片的右下角显示红色的“世复检测”四个字。